

My mother [60f] is going through something and fixating on "the one who got away" [60s, M] despite being married to my father [62M] and I am stuck in the middle.
I [30f] am currently living with my parents until I can get my own place, I have been here for about a year.
I knew my parents' relationship hadn't been great in awhile. My dad was in charge of finances and they lost the house, and ever since then, she has quietly resented the hell out of him. This happened 10 years ago and instead of seeking counseling or getting a divorce, she has slowly become an alcoholic who gets aggressive when she drinks. They have a lovely home in the town she wanted to move to after retirement, he still works full time at a job he hates so she can have good insurance. He does have some executive function issues and he is clinically depressed, so sometimes he just zones while she complains constantly, orders him around, and talks shit behind his back to me, their child. I have made my discomfort with that very clear and she has not stopped.
Anyway, something in her FB algorithm has been leading her into the cruncy granola spiritualism crap, and she decided to read her old journals to "try and find herself" as she was when she was happy, 40 years ago, in college. My whole life, she talked about her glory years in college and basically nothing else. But I didn't know about John (60s, M) until fairly recently.
She drinks and talks at people, that's how I know this. In college, she was very popular with men, and that was very important to her. She entered a difficult relationship with the man I would grow up knowing as my gay uncle, and then my dad shortly after, but she talks constantly about how many men asked her out and flirted with her and stalked her. I've hated hearing about it for decades, it is so gross and male-focused of her. During that difficult relationship, John began sniffing around. She and John have no boundaries and never have. She is now saying that the ex, a man I love as family, is "bad karma" that kept her away from John, and my dad was a "rebound." She says John is her twin flame/soul twin.
Important to mention that John is also married. Mom told me she's been talking to him, and his wife. They even went on a "double date" which ended with my dad and John's wife standing by awkwardly as they gave each other a 5-minute hug.
I think this behavior is fucking disgusting. I have told her outright to stop talking to me about it, to seek help, that she sounds like she is on the verge of a mental break. Of course, that didn't help, but at that point I was heated from hearing her wax poetic about how disappointing my father is. She cries and apologizes for telling me such awful things, says she is so sorry for hurting me, then keeps fucking going.
Edit to add: this is not menopause or perimenopause, she went through that when I was in high school. She had a total hysterectomy last year, so I low key wonder if her hormones are fucked up regardless.
Am I losing my mind, or is she?