I may be repeating some of the things that GG just wrote, I didn't fully read her post, but here are my thoughts --
Try to see things from his point of view. Imagine that your wife is sex negative, and that this has always been a point of pain for you. Over the course of your marriage it's sometimes made you feel unattractive and unloved by her. However, you've worked through those feelings and came out the other side stronger. The way you did it was by telling yourself that it wasn't *you*, it wasn't that she didn't want you specifically, this is just how she is, she's just not that interested in sex.
Then this new dude comes into the picture, and suddenly she *is* interested in sex... way more so than she ever was before, in fact. It turns out that all these years? It WAS you that was the problem. All the things you told yourself, all the ideas you still relied on to make things okay, were false all along. She wasn't disinterested in sex, she just needed someone to be excited about... and that person wasn't you.
Cut the guy a little slack, have some sympathy. You come off as very disdainful towards him. Push over, indecisive, weird, wishy washy... and maybe he is all those things, I don't know, but geez... is it possible that he's picking up on your real feelings about him and that that's making it harder for him? To not just be shown up in terms of his wife's desires by another man, but to have it be a man who doesn't even respect him?
Take deep breaths. Be calm. You have what you want, right, intimacy with this woman, at least to a certain degree? You're blessed, in most cases two divorces would be happening right now. Focus on the good stuff you've got, be grateful to the people -- your wife and this man -- who've made it possible because of their love for each of you -- and let this poor guy heal.
Me, 30ish bi female, been doing solo poly for roughly 5 years. Gia, Clay, and Pike, my partners. Davis, ex/friend/"it's complicated." Eric, Gia's husband. Bee, Gia and Eric's toddler.