Y'all wildin'

My girlfriend and I have been together a little over a year, and it's always been rocky. We've broken up many times (almost always me with her) but then we end up back together in a few days.
She has never hit me until today, and then suddenly slapped me after she held my shirt and pinned me against the wall. FYI - I did nothing to her in retaliation . However, I feel pained and disappointed by her action.

Reason - she saw me with a lady who was supposed to apply for the post of a chef at our residence and thought I was having an affair .

I explained myself and next best thing she said to me was that she is done with the relationship.

What do I do?