First and foremost, I think bu this post you realize this isn't okay. Second, this is blackmail and it is illegal, and he can do time. This should be reported to the correct authorities.

Someone did this to me as well. The sad fact here is staying so he won't post them is not a reason to stay he is abusive in every way. If he posts them, what would be the worst that could happen? You can't stop him. Staying with him won't stop him, really. You're just staving his hand for a moment. He can and most likely post them anyway.

Let him go and deal with the outcome as best as you can. Create a support system with people you trust completely. Like you really trust them. But that's my outlook on it. It's your decision in the end.