I'm going to take advantage of my girlfriend after she cheated on me
Why do you want to take advantage of your girlfriend?
I want to beat her up badly
It seems like you were really hurt by what she did to you. Still, taking revenge on her by doing the same is not going to help things.
Fuck her. She hurt me badly.
Don't let her infidelity make you do something you will regret later. She was in the wrong here, you should try to give yourself some space from her and mull over your emotions before doing anything rash.