For context, I’m in a singles group where people sign up to go to activities. I met Kevin (38M) last April while I was still in a different relationship. When that relationship ended Kevin immediately started pursing me. At the time I wasn’t aware but he was also aggressively pursuing my two best friends (32F and 24F) as well. Which caused a rift in our friendship that only go better after he and I had broke up.

By June/late May of last year Kevin and I were basically in a relationship. We’d select what events we were going to go to together, he’d basically never leave my side. He would bombard me with compliments and attention. We were dating for a few months when he suddenly got really cold, and started making weird comments during date nights. Ex. We were watching a comedy special and the comedian made a joke about it not being smart to date “10s” because they’re all crazy, Kevin said “yeah that’s why me and my ex wife aren’t together she’s a total 10”. (For reference his ex wife is about 5’4”, Blonde, and very thin. Me and this newer friend/acquaintance are a little taller, brunette/multi colored hair, on the curvier/more plus side) I brought up doing this thing I had read about “25 questions to fall in love” it’s basically just like intense get to know you stuff, and the psychologist that wrote it theorized that you only needed to know the answers to those questions to fall in love with someone. He got really weird about it. He’d also get mad if I was talking to anyone else (entirely platonically) at events but would get weird when I called him my boyfriend around our mutual friends.

He called me in mid August to meet for dinner after work, and said “I think we should discuss if we both still want this” right when I showed up. We talked through dinner and I thought had assuaged any issues (we had planned out things to go to for the rest of September, we planned a day to go to the Ren Fest together) so after dinner when he invited me back to his for sex I was all for it. I went home that night and he texted me at 6am the next day saying that we needed to break up. When I asked for clarification he basically spent the next hour telling me all the reasons he thought I was the last person he’d ever fall in love with. He listed that he hated kissing me, that he didn’t think he’d ever be able to get past our age difference, that I was clingy and needed to be reassured all the time, and basically implied that he had never actually been attracted to me because of how I looked (heavily implied that he thought I was fat), he also admitted that he had felt that way the evening before but he just wanted sex so he told me whatever he thought would get him that.

Most of our mutual friends ended up kinda cutting him off, not through my suggestion, but just at their own decision when they got the situation explained to them. He ended up basically getting kicked out of our mutual friends D&D campaign we were both in.

He basically didn’t come to any events in the singles group for months. I didn’t see him at an event until January of this year. We both just kept our distance.

This is where my newer friend/acquaintance comes in. We can call her Amanda (26 F). Amanda joined the singles group in late February/Early March. We met at one of her first events and hit it off due to our similarities(one of our friends joked that we could be sisters). We ended up planning to go to another event together, and hung out there .we made semi-plans to get a coffee or see what events the other was planning to go to when I returned from a trip at the beginning of April. I was out of the country for two weeks until mid-April, and then ended up catching a fairly bad cold on my way back so I didn’t end up going to another event until this last weekend. I got there and saw Amanda on the couch and was excited to see her until I saw that Kevin was seated next to her with his arm around her. One of my best friends was also there and she immediately saw where I was looking and said “oh yeah, that’s a thing now”. I guess while I had been gone they met at an event and Kevin basically had been doing to her exactly what he did to start our relationship.

I’m struggling because on the one hand Amanda is an adult and she can make her own choices about who to date. But on the other hand if I just started talking to someone and someone I knew, knew some pretty awful history about that person, i’d want to know.

I’d obviously never tell her to break up with him if it wasn’t her choice, but I also am feeling like if I don’t at least mention something to her I’d be a giant AH if this follows a similar path.

TLDR: went on vacation, when i returned a friend I had just made before I left is dating my semi-abusive ex boyfriend. WIBTAH if I either just ignore it and let it play out or if I tell her and she breaks up with him?