You and I are in the same boat. I've already been too around 5 or 6 wedding's of friends. One has already ended in divorce, complete shock long story. I'm in a wedding Labor Day weekend, and between May and July of 2007 I have 4 weddings, 3 of which I know I'm in. The last one is a toss up. I wouldn't be surprised if I was in it, I wouldn't be surprised if I wasn't.
I'm just glad I'm real close to quite a few. Every Friday I still get together with one group of friends for dinner. One set are married and the other are engaged. They never make me feel awkward, and we still have a blast. They may be married or on the verge, but they know they're still young and still have fun.
But as the time goes on I only feel the same as you do. It sucks to be the "nice guy", but I've tried going the other route and not being true to yourself is just wrong and you feel worse. As you may remember many of my depression posts between '04/'05 I've gotten past that.
As for your parents age difference, that's somewhat similar to my friends. They're not married or engaged, but they're expecting a baby girl at the end of the month or beginning of September. He's 25, she's 34.
I have my day I'm down, but usually snap out of it pretty quickly. I just keep praying, watch a little Joel Osteen here and there to remind me things will only be worse being negative, excercise, and keep busy.
I have plenty of reasons for wanting to move forward in life. But last weekend I had a talk with my cousins husband about staying in the real estate field, but getting into the commercial side of it as opposed to residential. It takes a lot for me to show my enthusiasm for things. I can be jumping for joy on the inside, but won't show it outwardly. Well now I'm thrilled to death about the possibilities of my success in the near future. That's all I can do is go on with my life and succeed for myself. Once that happens everything else will fall into place. That's my belief and that's what I'm going to keep doing and thinking.
Best of luck to you man. Hang in there, it'll get better. Trust me. And remember I'm as miserable as you!