High Treason,
I'll probably be the first of many to say this, but you're wrong. Physical abuse should never, ever be an acceptable way to communicate. It is the way of the bully, of the violent, of the abuser.

Shauna,
There are a couple of options:
1. As he's never done it before, something may be bothering him. You could sit him down and get him to talk to you about what caused him to act this way. If he's truly sorry and is willing to seek some help, then you may be able to stay. If he ever does it again, get out.
2. If this is just an escalation of the way he's been treating you recently, then you need to get away from him until he's sorted his head out. A trial separation at least may be needed.

Whatever happens, you should never be afraid of your partner. If you are, things are terribly wrong and you need to consider whether the relationship has a future.

I'm really sorry you're going through this. My best wishes and s to you.