I don’t think it’s ever too late to apologize for something you did wrong. It is noble of you to want to do so. In this case I’m not sure it’s a good idea, though. Consider this:
1) Do you want to be in contact this man again? He was abusive, after all. Apologizing to him is a nice thing to do, but not mandatory. Is it worth letting him back into your life, even briefly?
2) I hope you don’t believe that his abuse was caused by any behavior on your part. It doesn’t matter how big a “bitch” you were; abuse is never deserved or justifiable.
3) Be sure that your your reason for wanting to apologize is that you truly regret your mistakes, not because you are hoping for an apology in return. That may or may not happen.
You had a tumultuous relationship. You both did things wrong, and you realize your own role in it. That might be enough. Live, learn and move on. Unless your guilt is holding you back emotionally, I don’t think reaching out to an abusive ex is worth the potential problems it could cause. Think it through very carefully.
Thanks for the question.