It was a happy ending. The wedding proved a success: tons of friends and a completely in love bride and groom. It was amazing. Surreal actually, to see him so . . . happy.
A "Happy Ending" as opposed to An Interesting Resolution means that your ex-boyfriend will give you a huge hug after his wedding and thank you for coming. It means you can say "my pleasure," and actually mean it. It means you can cry with joy for each other.
And it means you get to see old friends...