In my opinion, these statements are always a bit generalized. It depends on the position and where you work.
For example on job stability/security:

There is definitely more stability in the sense that your contract is not temporary. On the other hand, I did an internship once in a company where I felt the pressure on the researchers was quite high and there was apparently a high turnover rate regarding the project leader positions. Now you may say fair enough, if your performance is bad you lose your job in academia as well, but I had the feeling that there is more understanding that projects sometimes turn out to be less promising than initially hoped ("that's science!)

Generally speaking, there is definitely more money in industry, but again that completely depends on what kind of position you have. If you are a senior scientist at Roche in Switzerland, you probably have an incredible salary, but I also see people leaving my institute and working in industry for a salary that is lower than the post doc salary at my uni.

Life sciences is a broad field, so only you will know how desirable your set of skills is for industry. If you have a lot of opportunities you might continue looking for something "better" or higher in the hierarchy, but as far as I know many Life science graduates are happy to find a position at all. In general, I don't think you have to worry about taking a job as a research assistant. It can be a good way to enter a company and if you perform well and have the necessary qualifications, you might move up quickly. They rather promote a research assistant they already know to full researcher than hiring an outsider for a researcher position. Also, higher positions require Industry experience that Uni Post Docs don't have.

If it's a lab-based PhD, this is not so incredibly unusual. In case your project is not working well because hypotheses turn out to be wrong, you try different approaches or work on a "safer" project that is more likely to yield a paper. After two years you may argue that there is still enough time to create enough data for a thesis and they let you continue. Suddenly you are 3.5 years into your PhD and they tell you that it's now definitely just not going to be enough to pass. We had someone like that where I did my bachelors. Even the supervisors felt really bad for her and said that she did a solid job. I guess she was just a bit unlucky with her project. Everything but the safe project failed.

I would also check with others for a second opinion but in case it is going to be an Mphil, I wouldn't worry to much about the CV. There are tons of students who study much longer than the estimated time for the completion of the program. I have several friends who took 8 years in total to finish bachelor and master degree even though you can do it in 5. They traveled, worked part time or were simply a bit lazy.

Don't despair and good luck for the future!

I honestly don't understand why you even consider to leave.
Most of what you say is relatively normal. For example, It is rather uncommon that supervisors beyond the post doc level have the time to show you techniques in the lab. Most of them probably haven't been working in the lab for quite some time and are therefore anyway a bad choice to learn new techniques. Most of my PhD colleagues have a meeting with their boss every 4-6 weeks where results and future experiments are discussed but besides that, they are on their own. You can always ask colleagues for advice but to some extent you just have to acquire the knowledge yourself and try it.

Your PhD is going so incredibly well that you could write up and finish in 1.5 years. This is exceptional, whether or not you knew the techniques before. If you are really annoyed by the environment and your supervisor, then my suggestion would be to write up and search for a follow up position that provides you with more training opportunities. With a PhD in 1.5 years (many struggle to finish in 4) you should have no troubles to find something new

That is strongly depending on what you were doing during your PhD. If you have been doing advanced cloning, gene editing, development of new and complicated methods and so forth: great. Your skills are useful. If you've been doing a lot of repetitive and rather low profile molecular biology (PCRs, extractions, blots, transformations...): more difficult. The problem with the latter is that companies are not hiring someone with a PhD as an e.g. research scientist to do these kind of repetitive tasks.

In general, I could really relate to your post, as I often feel the same. So far, my project has also included a lot of repetitive work. It is necessary to get that data but it also made me wonder how that would qualify me for jobs in e.g. industry. I think that is a very common concern. As you don't want to relocate: What kind of jobs could you do in the area? Is there relevant industry? If not, this is anyway no option. Have you considered working in sales or as a product manager for a company that produces products for the life science sector (Quiagen, Promega....)?

First of all, I think it is already impressive that you made it this far despite these massive set backs in the project and the difficult personal circumstances. You can take pride in that. Many people would have quit by now.

Now that you are already over the 3 year mark (I just assume 4 years funding), why not at least try to write up and attempt to finish? In my opinion, there is not much to lose now. Have an honest discussion with your supervisor, where you also mention the difficult private circumstances and maybe there is a way to make it a thesis, even though the project was supposed to go further. Most theses have chapters where everyone involved knows that this manuscript is never going to get published. Chapters with negative results are quite common and as long as there is something (you mentioned one published paper) that worked, it can still pass. I would at least discuss it with my supervisor. Maybe he or she has an idea how to make it work.
I think it will bother you eventually if you quit so close to the end without exhausting all options.

Sometimes you also have to accept that certain things are just not for you. Some people need structure in their daily life and do great things when they have it. Others do exceptionally well if they have a lot of freedom and can organize their time themselves. Friend of mine studied a humanities subject that required very little university attendance. Most of the time you are supposed to do research for your assignments, which he always did last minute with the result of mediocre grades. He just couldn't motivate himself to start earlier at home. He often started few days before the deadline to work on an assignment they had 3 months for. Another friend of mine absolutely thrived during a similar degree and probably did much more than the degree required him to do. They are both intelligent. To some degree it is just personality.
You seem to have analyzed the issue quite well and know what the problem is, yet you didn't manage to change that behavior in 27 years. Unlikely that there is some magical technique out there. You just have to pull through and do it, but you already know that ;)

Do you really need that PhD to achieve your career goals? If not, maybe starting your own business or working as a consultant would be the better choice.

Did you discuss with your supervisor why you think that the analysis is inaccurate? Sensitive topic, but he should be able to defend his approach. If you see that the analysis is flawed, others will probably see that as well (assuming that you are right). Best case scenario the manuscript gets rejected right away. Worst case scenario you have to retract the whole thing later, which will reflect badly on you and definitely impact your career. Especially if you want to stay in that field, you should not consider a misleading publication with partially non reproducible results.

And you are the reason why this system is paying so little. There is nothing noble about working way below minimum wage in science and the fact that you are willing to do that does not make you exceptionally passionate at all. Science and a reasonable salary are not mutually contradictory and there is absolutely nothing wrong with demanding a fair salary for good work. No wonder that so many supervisors think they even do you a favor by letting you work for them for free. You advance their research and that's how they get their money, both supervisors and the University itself.

If you can't secure a position with funding, you are either very inflexible regarding your location or you are not competitive. No reason to get insulting just because you are frustrated...

It's hard to say something without more details regarding location or field of study but in Germany for instance, it is normal to get a 50% (around 1200€) to 65% (around 1500€) positions in the life sciences. I never heard of any scholarship that provides you with more. You are of course expected to work 100%. Only fields where it is really hard to recruit PhD students such as computer sciences will offer higher salaries.
It's of course disappointing if you expected a higher salary but in most of central Europe you should be able to live comfortably with 1500€. I know many PhD students that are located in Zurich and can promise you that even in Zurich, you'll get by with 1500€. I know several PhD students from South America and Asia personally, who came with their own scholarship that is in this range and they spent 4 years in Zurich. And no, there are no rich parents in the background that could afford to sponsor their child ;) You will live like an undergrad without any luxury but you can certainly manage to get by. I am however relatively sure that they will adjust the amount of money to the Swiss living costs. At least it was like that for a friend of mine with a French scholarship.

Personally, I would suck it up. If you have enough to make a living (and 1500 is enough) then it is all about the institution, your bosses, your project and the colleagues. That's what is impacting your mental health in the end. More money is always nice, but I guess you didn't get into a PhD program to earn a good salary ;)

What exactly are your career plans and what would make you happy? Who knows, maybe you guys aren't even a couple anymore in a year from now, so I would be careful to make such an important decision for someone else. If you don't want to worry about money and really prefer a job over the PhD then go for it, but don't do it just to support your girlfriend.

Any chance to reduce your current costs? London is of course extra difficult....if you move further away to save money you probably spend those savings on transportation...

It is a bit hard to give advice without knowing anything about the kind of financial issue you are in. I respect that you don't want to talk about it but the responses might be more useful with a bit more information.

How much money would you need compared to the 18-20k and what are the chances to land a fulltime job after quitting your PhD that pays you the amount you need? You mentioned that it would be hard to find a proper job with your background.

If there is absolutely no way to reduce your expenses or increase your income then finding a better paid job and quit the PhD seems to be the only option. In that case I wouldn't worry too much about the company or your supervisor. PhD students quit all the time and supervisors are prepared for this possibility.

That's what I would do as well. I am not a fan of these super long acknowledgment sections where people prate over several pages thanking literally everyone remotely related to that life period. My family provides the support they always provide, no matter what I am doing. I am incredibly grateful for that, but they give this support PhD-independent. I am pretty sure none of my family members or friends would expect me to mention them personally and all would be fine with a sentence like "Thanks to all my family and friends for all their assistance and support". They try to understand what you are doing and they show some interest in my PhD (some a bit more sincere than others) but that's where the supports basically ends. That's all they can do and they don't have to do more in my opinion. Of course it kind of helps me indirectly during that PhD time to have a loving family and friends but the people who really directly help me are rather colleagues, supervisors and partner and those are the people I would address a bit more detailed. But that's just me.

If you don't want to thank your father this is perfectly fine. We are just talking about an acknowledgment section. I would not overthink it. Do whatever feels right.

I think it's quite evident that this is all not like you expected it to be and doesn't make you too happy. Being just 5 months in, quitting isn't so dramatic. If you quit after 5 months you can just say you realized the topic is not for you bla bla bla. In most cases this is not seen as a failed attempt and won't hurt your career. You wanted to change something, took initiative, it wasn't for you, so you are changing again. Perfectly fine. This gets of course more difficult the longer you are pursuing the PhD. I am now 1.5 years into my PhD and have to say that if it is not overall a positive experience, it is not worth it. Too often you read about the PhD journey of people and it reads like a period of suffering and anxiety that you somehow survive and that's the value you can draw from it. If there would be great job opportunities afterwards, I would accept that as some sort of necessary evil, but there aren't. It is highly competitive and most people don't end up in research careers but in jobs you don't need a PhD for (and even having a harder time to get those jobs compared to non-PhDs). I am not saying that a PhD is always fun, but if you don't like to go to work and feel anxious during long periods then there is something wrong, even though many people seem to think that this is normal and kind of like you have to feel during a PhD.

Do some thinking if this is really what you want. Doing it just to avoid that "fail-stamp" is not a good reason to continue ;) Good luck!

Job-wise, I think it goes on until you have a permanent position. PostDocs and PhD positions are temporary, so some people, at least subconsciously, don't see them as real jobs but rather a continuation of your studies. Relocating to different countries every two years is also not really signaling stability. I can somehow understand that, especially when you grew up totally different.
The kids-thing goes on until you reach an age where it gets rather unlikely that you become a parent. A friend of my mom said she didn't want to have kids already when she was 20 years old and people said she would change her mind. They said that when she was 25, 30 and 35 as well. They thought the biological clock would kick in at some point and I think she got the kids-question until she was mid 40. And even then it didn't really stop but changed to a little bit of pity (especially when it's an event with a lot of parents and children...you must be heartbroken!) or even reproaches to be selfish from sides of the grandparents. Of course it depends on the family. Some families don't say anything as long as you are happy, others make their peace with it quite fast and some others never stop to bug you. However, in their defense one has to give them that a lot of people in fact change their mind on having kids in their 30s, so I understand if the parents are maybe still hoping ;)
I guess everything that is not absolutely common is strange to many people. Someone in my old department once said that his parents frequently complained that he is not moving to a more quiet neighborhood in a nice house. They preferred to live in a rented apartment in the city. He was married and had two kids, but still, this one tiny detail seemed to upset the parents :D

You are probably not the first guys to look at a disease using a sequencing approach. If you are absolutely sure that it does not matter, then maybe you can find some papers to support your point. It always helps me when my supervisors propose something that I don't agree with ;)