My cousin has been in an LTR w/ her (currently on) bf for the past 4 years. It's apparently drama filled and from what she's told me he's very jealous, controlling, and pessimistic. Which I assumed were beta traits.

From what I've heard he subtly puts her down although never physically but they definitely go through periods of peace then constant fights. She breaks up with him but he begs/manipulates (isn't neediness BP?) her back and it's all good again. She tells me she truly loves him and that its hard for her to stay mad at him.

I really don't know how long this could last for her mental sake and our family hate the guy but nothing we can really do to knock sense into her.

What exactly is the psychology behind this cycle? I guess there are healthy and unhealthy ways to keep a girl hooked like that?