My best friend’s affair has given me the ick. How do I get past it?

With advice from Sense & Sensibility and Forster's Aspects of the Novel

This one is about friendship… So me and this other woman have been friends from almost ten years, from years 5-8 of that I'd say we were each other's real number one support, shared so much, made future plans and it felt like the most committed relationship in my life. During that time she started seeing someone who I don't totally approve of - he's a lot older and was seperating from his wife but essentially cheating and keeping their relationship a secret. I felt distrustful of him, and angry at feeling complicit in their dodgy behaviour, but also didn't want to be too judgemental and hoped it was a short fling. After two years their relationship is now an open thing and she seems really happy. In that time some of the big life plans we had together didn't work out (thanks to covid). Instead, I've moved cities, made new friends, and we've kind of drifted. I thought it was just the distance but even when I go home to visit, I can't seem to get over this "ick" I feel, and it’s stopping me wanting to spend time with her. There's such a history of sisterly love between us but is it in the past now? Do I try to repair the relationship or do I just let it go?

CS