Ugh, I know how this is too. I avoided my friends for a while because of weight gain, and ultimately it hurt my friendship a LOT. One of them I don't know if I'll be able to recover.
SO GO! See them! Have a good time!
I just ran into an old friend of mine from High School a month ago. I was SO excited to see her again. Yes, she gained some weight. Yes, I did notice. No, I didn't comment. And NO, it didn't change my view of her or did it effect how good a time we had. Things were just as they always were. If she were to hide away and avoid me... I would have been so sad, and I'd miss out on seeing her. It would only drive us a little more apart than we've already been...
So please. See them. You'll have a good time. Be yourself. (And heavens forbid, don't text on your cellphone the whole time!! That was the only thing I disliked about re encountering my friend. Texting in the presence of company--especially a friend you haven't seen in years--is SO rude [/tirade])

You'll regret it if you don't.