My former best friend/roommate got into a relationship like this. He was living with me when he started dating her. She seemed cool at first, but then we slowly started to realize that she was straight up the insane controlling/possessive type. Like, the whole relationship was fucked up from the start. When they started dating, he was 32 and she was 20. He was her first boyfriend, and worse, first sexual experience as well (and did I mention that they fucked on their first date? Yeah. I know because I COULD FUCKING HEAR IT, by the way). So she ended up getting all crazy possessive over him and started to insist on spending every waking moment with him. She stayed the night almost every night, which of course meant that they would loudly fuck in the room next to mine every night as well. That was wonderful.
Anyway, shit only got progressively more fucked up. First she straight up tricked him into marrying her. Basically, he's had seizure problems nearly his whole life and needs meds to control it. Very expensive meds. Well, he ended up getting fired from his job, and as a result lost his insurance. So she convinced him that marrying her so he could get on her insurance was the best way to take care of that little problem. Despite the fact that there were PLENTY of other avenues he could have taken to get the medicine he needed. But nope, she got to live out her fantasy of marrying her first love, by taking advantage of the fact that he needed his life-saving medicine, and that he had started to worry that he wasn't going to be able to find anyone else at his age. THEN she convinced him to move out suddenly and get an apartment with her, leaving me completely fucked on bills/rent (at least, so I thought, turns out everything worked out just fine for me and I'm arguably better off now than when he lived here), despite the fact that she was the only one working at the time.
And how did that go? About as well as you'd expect. It lasted about six months or so before SHE got fired too (for being caught texting him while she was supposed to be working), they lost the apartment, and she dragged him off to another town about 30 miles away to live with her parents. And neither of them drive, by the way. So yeah, I haven't seen him in a couple years now, but the last time I did, he had gained quite a bit of weight as a result of doing nothing, since he always had to be around for her. And he's been stuck living in a town where he knows NOBODY but her and her family. And I won't even go into how she cut him off from his own family, as well. I'm good friends with his sister, and she fucked up their relationship SUPER bad as well.
So yeah, good times, huh?