What if I accidentally abused my girlfriend?
I hope you're joking, what exactly did you do to her?
I slapped her, because she pissed me off!
Even if your girlfriend made you angry, you should not have slapped her. If you are losing your temper then you should walk away and take a breather.
But she can get mad at me, right?
She can get mad at you but she can't hit you just like you can't hit her. Slapping her is bad and you could get arrested.