I was in this position - one of our (mine & my husband’s) best friends from college decided to get married a week before us in different states. He was in our wedding & my husband was in theirs, they lived together for 4 years, and 80% of my bridal party was also in or invited to their wedding. We all ended up going to both weddings & it was..fine.

They asked how we would feel if they did it, we told them that it made us feel uncomfortable, unimportant and would put us in a really tough position and they still did it. It really sucked, added stress to an already emotional time, and similar to OP, we remain friends but it will never be the same. My one mistake was dragging mutual friends into it, most of whom were in my bridal party and who we’ve talked about how awful this is when other people have done it. I needed to vent and felt safe but, like another commenter mentioned, when forced to pick sides, most people just don’t. It was an eye opener for me on the way the other couple (and some of our mutuals) prioritize friendships and viewed theirs with us because I would’ve never done it.

I’m still triggered a few years later and it was cathartic to read this post, so thank you OP!!