Please help with etiquette issue? Not sure what to do?

Ugh, I wouldn't want that guy either. Just tell her she should have waited for an answer before he got his suit all ready. I think she will come around and eventually come to the wedding, especially if this isn't her boyfriend. It is NOT approrpiate for her to bring her "friend with benefits" to witness the union of your love. I wish you all the best with this but it's YOUR day, if you don't want him there, don't have him there.