Have you guys ever experienced this before?

[Elysiume]

There's some unclear antecedents in your post, which makes an already confusing situation more confusing:

One of my group straight up said he's leaving because of it. (And apparently it was just the straw breaking the camel's back of him skirting the rules.) The rest of the group says that everyone, including me got onto him about it. (I don't tend to do that.) But they don't remember what he did. He didn't show up last session, and isn't responding to messages.

Am I reading this correctly that pronouns 1 and 5 are the person who left and pronouns 2, 3, and 4 are the person who committed the rules violation? Or is pronoun 3 also the person who left, and he caused some sort of kerfuffle during the session?

Seems like an all-around weird situation and the person who may be most likely to know details is the one person you can't contact (assuming 1 and 4 are the same person).