My friend used to assault his gf. Why do some women tolerate such people?

I won't call him exactly a friend because I too had confrontations with him. He was more like classmate. We were all from north, studying in BLR.

So, this guy and his gf were in relationship since class 11 and took admission in same college, same branch to stay together. I also got admission in the same place and that's how our 'friendship' began. In 2nd year, they shifted out of hostel to live-in. I too moved out and started living adjacent to their flat.

Soon after there was a big fight between them, just like married people drama and I had to mediate. I was naive and all this was shocking to me. I told him she will leave you after this. His reply was 'Where else will she go?' in an evil tone. At that moment, I realised I was with wrong people. Years later, I had a fight (not physically) with the guy. I just wanted to get out of college and never see him again.

These kind of quarrels were very frequent between them as I can hear him abusing, hiting her and she crying. COVID happened, we all went home. Came back after 1.5 years and things became even worse. This guy used to behave like a 40 year old drunk husband at the age of 20. She used to say things like 'Never ever my parents hit me, why do you beat me?', 'I will never marry you if you continue to be like this'.

I could hear all that because we shared a common wall. I felt sad for her and amused at the same time. Why is she tolerating an abusive, egoistic narriccistic idiot? She is not married to him. There is no social taboo to break up.

It's been many years now and they are still together. I am no longer in touch with them, don't even want to.

I just want to say this - she was kinda cute. I had feelings for her , when I saw her on the first day of college. After I got to know they were together, it all vanished and I just maintained friendship. I hope people don't judge me bad.