[SOPi_Jawbreaker]

Adding to what Drolefille said, there's also often self-esteem issues. In most cases, the physical abuse doesn't just come out of nowhere. Oftentimes, it's accompanied by, if not preceded by, mental/emotional/psychological abuse. Because, if a guy acts all wonderful and then out of nowhere starts smacking his girlfriend around, she'd probably think he's a psycho and get the hell out. But when it starts small, like with him complaining about her or the things she does, it'll sneak up on her. And he's able to do and say worse and worse things to her. And if someone's constantly told that they're not good enough and that no one else will ever love them or want them, it eventually erodes their self-confidence and they start believing that no one else will ever want them.