How to have the courage for a friendship breakup?

I have been friends with this person for approximately ten years, we met in early highschool and now we are both 24 years old. Our friendship hasn't been as close since I moved from the smallish town we grew up in to the major city near us but we've kept in touch mostly over video chat and very occasional hangouts. I think she still considers me to be one of her best friends but over time I've found we have less and less in common but I've held onto the friendship.

A couple of months ago, she invited me to be her plus one at her coworkers wedding. I didn't have any amount of fun and was really bothered when she told me that the coworker who has getting married has said transphobic and racist things in the workplace on many occasions. She said that this really bothered her yet she also seemed really happy for her getting married, bought her a thoughtful gift, and still accepted the invitation. I didn't say anything that night about what I felt about that and now it's been months of me bottling it up and putting very bad effort into making plans to chat/hangout. She has continued to reach out the past few months so I know I can't just let things fizzle out and I wouldn't feel good about that, even if it would bring the relief of not having a confrontational conversation.

I feel like our values are too different to keep being friends. I think allowing a coworker to get away with saying such shitty things and not speaking up is a form of accepting those things. I just don't know how to express this without feeling like I'm on a high horse. In a way, I feel like I'm in the wrong because maybe I haven't expressed enough in the past how important anti-oppresive values are to me and that I have the expectation that the people close to me also act on those values.

Have you ever broken up a friendship over different values? I feel like I'm the asshole for bringing this up out of "nowhere".