My two closest friends are my college friends and weight was never a factor in our relationships at all. We were best friends instantly from circumstances, thrown together in a dorm and sharing similar interests none of which centered around anything active.
I was the smallest of the group, which was sometimes commented on, but really only as a matter of fact. We've all gained weight pretty much pound for pound so our ratio remained constant, which is weird. Now we're all losing it together. One has lost 75 pounds right along with me! The other's loss is a bit slower but she's doing the best she can. And none of it matters.
I have no other "friends" and I've never felt weird about being the fat one other than those feelings I put on myself.
There is another "fat phenomena" I find interesting which is that if your friends are fat, it's more likely that you will be too. I fit that. Look at how my friends and I gained weight together pound for pound! We all gained 100 pounds from the time we met in the same amount of time. How weird is that?