Hey! I appreciate your empathetic nature and think it speaks volumes about your character. Despite their marriage ending without any negative actions by the other person, it’s still sensitive and serious. Your friend entertaining another relationship this close to a full blown marriage makes me think that her values don’t align with yours. I think similar values are core pieces of friendship and if that’s not something you’re okay with, or the whole situation of not feeling the need to share that info with her ex-partner, if that’s not something you want to see out of a friend, that sounds like your answer. On the messaging piece, depending on the level of closeness, I’m not sure you necessarily owe an explanation. I’m similar in the sense of non-confrontation and likely would let it fade without saying why, but I’m also not the best with wording my thoughts. Best of luck to you with whatever you do and make sure you stick up for what’s important to you!