Worthy of a breakup? Did I overreact?

So I've been with this girl a couple of months. We are at a party the other night, and she was pretty much irritated at me all day (she wouldn't say why, which is one problem I have with her - never expresses things directly). So I had some built up frustration... anyways, at the party she pretty much went off and did her own thing. I catch up with her, and some drunk guy is invading her personal space (to the point where she needs to move her head back to avoid his drunk blabbering). So I move in and tell him nicely but sternly to "step away" - he said "f*** off", so I pushed him (not realizing how strong my push was or how drunk he was, he stumbled to the floor). Instantly my girlfriend chewed me out, saying I over-reacted etc. She didn't want me to drive her home, said she would "get a cab" - so I told her, I know you are pissed but let me take you home, you don't know anybody at this party etc. She wouldn't have it, so I left - haven't talked to her since -was a few days ago