Hi,
I am second year PhD student in life science and am considering to leave the program in this May.
The reason I want to leave the program is the family issue: my parents are ill, and I want to be close to my family, and they also want me to be close to them. I actually made my mind to quit PhD, but have not told my advisor yet cuz I am kinda scared with his response. Since the new semester has just started, I guess it is good time to tell him I want to leave. What do you think?

I actually like research, so after leaving current PhD program, I am considering to go grad school in my home country (yes I am international student). So kind of transferring to another PhD program. I have not even applied to another grad school yet since application will start in July in my home country, so my plan is to quit in May and apply in July.

My biggest concern is the relationship with my advisor. My advisor is kinda difficult or severe person. How should I tell him I wanna leave? Is it a good time to tell? Any suggestion is greatly appreciated. Thanks

There probably is no good time to tell your supervisor.
Can you start putting feelers out to your home country universities about your chances of getting a post?
My thought is that because you are enjoying research can you hold on until the PhD is finished before returning home?

When you do tell your supervisor: focus on your parents health and not that you miss home and that your family want you there. The supervisor, although unhappy about your choice, is more likely to give you a good reference if it sounds critical that you return home for serious illness rather than you being homesick.

Hope it all works out for you.