I've found that I tend to have a few close friends that I've had for years, a boyfriend who is still learning about what it means for me to live with PTSD, and that's about it. I find the more I am able to focus, in general, the easier it is to study and to maintain friendships. When my PTSD symptoms are heightened, I tend to pull away as I find myself more in my head, or disassociated.
I think what I've found that works is finding people in my life who know sometimes I need to have my own space, and know that I would move heaven and earth for them - but sometimes I'm just not going to be there, not because I don't want to, but because I need to take care of me first. That has meant that certain people who were in my life, are no longer, but I have found that the friendships/relationships that have are stronger and mean the world to me.