I was in a abusive relationship for a whole year in the same house with his parents. They never found out. Eventually i told them but they would basically tell him "hey don't do that" and carried on. Eventually they would joke about it to him, and when I attempted to leave him his mom said "why are you leaving for it now when you've stayed this long ?".
I later found out he did it to his ex for several months, literally down the hall with his bedroom door open when he was in highschool.

Its scary to try and leave even when you have support. Do you know how many times he called me a "fucking retard" or that it was my fault he was hitting me? Countless times he'd say "its like you want to be hit by me" just because I would defend my side of an argument. I wouldn't have to say anything mean or cuss or raise my voice. He would just get so mad that I'm not saying or doing what he wanted.

He once got physical with me for being sad that he didn't do anything for me for valentines day (and later found out he was cheating on me with an ex anyway).

When you're treated that way by the person you love, it sends your sense of awareness, self esteem, and confidence crashing down. You always second guess yourself. Always wary and uncertain. That girl he cheated on me with was actually the other ex he abused. People like that know how to get their way. They know how to mentally manipulate people. Its also scary because there's the risk of police not believing you, or letting him out before court (with his ex he was free for a whole year until court and juvie). In that year he could have killed her. People like this know what they are doing. They aren't just some blind psycho.