Abuse is cyclical, it repeats itself, and when you get back together, they are on their best behavior. One should NEVER feel afraid in a relationship. That fear is real and it's because he's been abusive and you're afraid he will be abusive again, which he will, I'm very sorry to say.

Listen to what your body is telling you. FEAR. You're afraid of him. And you're sabotaging it because you know you shouldn't be there. Why did you even go back? Sorry to say, but that was a big mistake. Abusive people do not change. Tigers don't change their stripes. He only wooed you back in, pretending to be a different and a "changed" person. Trust me, he hasn't changed. He will abuse again. I'm very sorry, but get out, is my advice. You're going to do even more damage to yourself if you stick around to see it happen all over again.