You don't have to decide anything today or tomorrow or anytime until you are ready, no matter what that decision may be. I don't think it's that you will know when you are ready to leave, I think you will get to a point you decide just how much you will put up with and if there will be any change or not.
I am going to gently say that you post that your questions are rhetorical, however when you talk of the abuse you have endured and how can you trust this person again, it does not come across that way. No one here is going to recommend you stay with someone who abuses you on every level. However, no one but you knows just what you mean and what you can or will put up with.
I hope you continue to go to Alanon. Don't feel pressure by anyone as you have to come to your own place in your own time. Goodness, it took me 18years! That's a long time!
Tight Hugs....we are here for you always!