Throwaway for privacy. 

This is an old story from when I was in a friends-with-benefits relationship with a guy who turned out to be an abusive prick, but he’s not the one in the title. I’ll call him A. The title refers to his ex-girlfriend. I’ll call her B. (I’m a guy, btw.)

Backstory: The way I got involved with my ex-FWB was very wrong; he cheated on B with me. Theirs was an open relationship, and I was attracted to A, so I thought, “Why not?” They had limits—his ex was okay with manual stimulation: oral and penetrative sex were off-limits. We went further than that. (B was a childhood friend of mine, which makes it worse IMO.) I fully realize I’m 50% the asshole (50% because it takes two to tango) in that scenario &amp;amp; I cannot even fathom cheating ever again, and I haven’t. 

After I confessed to B that we had cheated (I needed to tell her the truth; I hate lying and felt awful for her), she and A had a constant on-and-off-again relationship. 

Their relationship was toxic even before A cheated; they were very codependent. (I’m talking “B posted an old video of them kissing on her public Instagram the day after they broke up the first time, saying she hated life without him and that she was crying &amp;amp; A replied in a similar manner” codependency.) B was verbally &amp;amp; psychologically abusive, whereas A was mostly psychologically abusive (manipulation and gaslighting—he did the same to me &amp;amp; took advantage of my mental illness to convince me that I was delusional). 

B would text me often. She has a traumatic past &amp;amp; tends to masochistically engage with people who have hurt her, so I tried to minimize contact as much as possible once I realized this. She shared intimate details with me, including that she was in love with this guy she called her “muse” and considering moving in with him. She later had sex with him. This was during a time when she was back together with A. 

I was still into A (hadn’t realized he was toxic yet), so when B dumped him &amp;amp; made him promise to never talk to me again (threatening him with punishment if he contacted me or I contacted him) since “she didn’t want him to move on, especially with me,” I flew off the handle and said she was controlling him &amp;amp; had no right—especially since they were broken up. I went to bed fuming. 

The next day, I shared everything on social media she’d told me not to tell A, since he followed me &amp;amp; if I contacted him directly he’d be punished (plus I was pissed). I didn’t include insults in the post; her actions spoke for themselves. I admitted that I had cheated in the post as well. 

B then blamed me for her heroin relapse (I shit you not), amongst other awful things. She moved away shortly thereafter, &amp;amp; I cut off A a few months later. 

AITA for exposing her publicly? At the time, A called it immature, but everyone who saw the situation firsthand supported my actions. I’m kinda expecting an ESH response but I really want to see the nuance of all your answers. 