Sister's boyfriend being so nasty towards my husband

My sister is dating this guy that she's so in love with. He's everything she wants. A good Christian man. This man despises my husband. There is lore there. My husband is a bisexual man. Him and my sisters boyfriend went to an all boys Catholic boarding school as teens and while he was also still very homophobic back then, he and my husband used to secretly hook up. I think he thinks my husband is going to tell the whole family which he would never do but this guy is disgusting. He has called me husband slurs. Said there's no such thing as bisexual men and how my husband will leave me for a man. Makes jokes about our sex life at holidays. My husband used to hook up a lot in his boarding school. It's actually why he got kicked out and he will talk about how my husband was the f slur of the school. Dude you were having sex with him too? My husband tried to talk to him and say if he's scared that my husband is going tell everyone he had no intention of doing that. That conversation went badly because he blamed my husband for them hooking up saying my husband clouted his judgement with sin. He's always being shitty and trying to hurt/embarrass my husband when my husband isn't even doing anything. My sister won't tell him to stop. My husband is just taking this as he hates himself so much so he's taking it out on my husband. This guy is just super annoying and he talks badly about my husband to EVERYONE. Makes fun of him. His sexuality. Says he's not super masculine. It's so weird

@Jamie my husband doesn't want me to do that and said he stopped taking it personally and things that guy got some shit he needs to worth through. Which obviously but I don't think he should be able to just be crappy.

@G I'm the only one that knows they used to hook up. My husband doesn't believe in outing people and neither do I but this guy is poking the bear for no reason. Even after my husband said he had no intention of telling the family anything

@Jenee when I said a good Christian man I should have been clearer. It's what my sister was saying about him. I think he sucks