Husband used to date my cousin!

My cousin moved in with my mom and when I went over there, the look my husband gave her told me something was up. That's how I found out they used to date when he was 19. He's 37 now. I was honestly pretty upset because I strongly dislike this cousin. I tried to let it go, she laughed it off. Well ever since I found this shit out she has made every opportunity to tell me what it was like when they were together. She talked to my mom about their sex life when they were together. It was super disrespectful and what made it worse, was stuff she was saying they did together, he wouldn't do with me. She's talking about bandage and stuff and he is a vanilla and likes plain vanilla sex. I have no problem with that, but the fact that he did bandage with my fucking cousin. She went out of her way to find old pictures of them together. My husband is now refusing to go over my mom's house because he wants to avoid the drama, but I'm close to my mom so I see her all the time. Idk why my cousin feels the need to continue to talk about their relationship together. I told her to shut up about it and she said I'm just jealous and he was her past so she can talk about it. I just had to ask my husband what is so different about me and her. Why was he okay with doing kinky stuff with her, but with me it's just sex. His excuse was he was 19. He did a lot of weird stuff. He said he didn't want to talk about this past stuff, but I was hurt. We argued about it and he walked out the door. When I asked where he was going he said "To sign back up for the military. Remind me to die this time!" Yes he is very over dramatic. I'm really disgusted by this whole situation