Hit for not smacking his ass

So my bf has admitted he has developed a drinking habit about 2 months ago I've been trying to be supportive well a few weeks ago he was drunk and he asked me to smack his Ass and I said no so he slapped in the face. I cried it hurt. "I was only playing around it wasn't supposed to be that hard" ect. I'm sorry blahblah. Whatever. Sure. Well he's talking to his bff now and he brought it up and they're talking about it and he tells the story and they're laughing about it. And it just hit me. You NEED TO LEAVE HIM now. He doesn't care. So here I go. Beginning a new future for my son and I.