I think I'm a bad person
What makes you think you're a bad person
When I beat my girlfriend. She doesn't deserve that.
You may or may not be a bad person, but hurting a partner is never okay. You should get some help with this issue, it's a really serious one.
I don't need any help. What happened with her is karma.
I'm worried that you're not taking this seriously given your last statement.  Setting aside the serious physical and psychological damage you're causing her, there's also the very real chance of you getting arrested for this.  You've realized this is bad and I seriously suggest you do something about it before something happens.