I'm not going to attend my good friend's wedding
Why won't you attend your friend's wedding?
I'm only close with him and not the bride.
Don't worry about the bride!  Worry about how your friend will feel if you don't show.  It's wrong to avoid important events in the lives of your friends.
I don't think he'll mind if I don't go to the wedding.
This is a special day for your friend and I'm sure he'll miss you if you don't go. Go to the wedding, you'll meet new people and have a good time. You may regret it if you don't go.