The best predictor of future abuse is past abuse. Your GF verbally abused you and so you threw a drink in her face. 2 abusive people and the outcome was physical. I doubt your going to turn into a serial killer from this but you've shown a pattern of consequences resulting from your anger. Some anger management and counseling could probably be useful. There is never an excuse for violence but some people push our buttons and part of being healthy is recognizing when people are doing this and backing away rather than engaging (((hugs)))