I think everyone is happy. Shawn said he wouldn't go if Bret didn't want him to, so now he won't. How do you know he even really wants to go? He'd probably just as much enjoy the night off. I'm sure he can find time to see his old friends and congratulate them if he really wanted to.
It's like a graduation. I'd rather not attend a friend's (I would have been happy not attending my own, for that matter), as they're long and boring, but I'd go out of respect. Maybe Shawn is actually happy that he now has an excuse not to be there.
Edit: Basically, Shawn agreed and had no real problems with it, so it isn't selfish of Bret. If Shawn really wanted to go but Bret refused to allow him, that might be a little selfish.