Unfortunately this doesn't only happen between two people who are dating. It happens with friends too. After I got really sick last year and ended up loosing my hearing, there are a few long time friends that want no part of me anymore. Maybe I scared them into thinking "wow this could happen to me" I was very hurt over this, but you learn really quick who your true friends are. Good Luck!!!!,
My mom discovered this when she had lung cancer surgery (she's great now, totally recovered). A "friend" of hers, who worked in the hospital, never even stopped up to see her. Mom has become really tight with who she calls a "friend".
I am thinking of how my friends would react if something like what happened to you happened to me. A few I bet I would never really see again. Maybe one visit, at first. My thought about why is they would feel we really had very little in common anymore, or that it would be painful to see me struggling to communicate with them. Like being with them would be rubbing it in what awesome times we had chatting and joking before and this changed everything. I can imagine they would feel uncomfortable, like they're making me struggle. I'm guessing that your friends weren't trying to be mean to you by leaving, some probably thought they were doing you a favor, oddly enough. Others, well, they just suck.