Dilemma - to be in friend's wedding, or not

[NWguy]

I've been asked to be in a friend's wedding this fall. He recently got engaged over the holidays.

The problem is I don't like his fiance. I share this sentiment with mutual friends, some who've distanced themselves from him because of her. In the early part of their relationship, she was very controlling and divisive; she never wanted him to spend time with his friends - a few years ago, she sent me a DM via Facebook and thanked me for inviting my friend on a camping trip, but said "he regretfully cannot make it". He later told me that he really wanted to go, but she put her foot down.

I'm happy for him, really. But I don't want to be in this wedding, and neither do I want to attend, partially because a few mutual friends have been left off the guest list, and also because only within the past year has she attempted to befriend me.

This has never happened to me before. How do I convey this to my friend without hurting his feelings? Could this possibly damage our friendship? Or, should I suck it up and stand at his wedding anyway?