I had the urge to assault a waitress at Denny's last week and I just got released from posting bail, but I lied to my girlfriend and told her I was on a fishing trip with my friends all time.
Why would you feel the need to assault the waitress at Denny's?
She wasn't paying attention to my needs, I was too angry to deal with things at that point
It's wrong to assault a waitress just because she wasn't being totally attentive to you, and it's almost as bad to lie to your girlfriend about it.  Your girlfriend needs to know the truth about you, so she can make up her own mind about whether you are safe to be around.
You should have seen this waitress, she was dressed like a slut and I bet she's a gold digger.
It doesn't matter how she's dressed, you have no justification to assault her at all. And on top of that you're lying to your girlfriend about the situation. Need to be honest with her and tell her what happened before she finds out.