This scenario sounds very familiar to me...
Lots of times they CAN be very charming, nice and even sweet but the ugly, cruel alcoholic behavior always comes back to the forefront and unless he stops drinking this will happen time and time again. I put up with so many mood swings and downright rude, obnoxious behavior but he always had an excuse that I bought into (I am stressed out, I am depressed, etc). Manipulative is absolutely correct, they have a way of making you feel sorry for them by playing the victim card.
I did this for 3 years because I really loved him and I wanted things to work out. Truth be told, there were times when he was better and it's the good times that keep us holding on.
I think when you're in a relationship where you cannot trust the other person and they are constantly saying thing that are hurtful it's probably time to get out. What does your heart say? Do you really think you can buy into any more empty promises? I think you know what the answer is there.
I got sick of my A lying to me about how much he was drinking, spending all of his money at bars and generally being a doormat because he was so emotionally unstable. I could not picture living the rest of my life that way.
So I went to see my therapist on Friday, she told me you have to pay attention to people's behavior, he is showing you how he is and you're in la-la land hoping that he will turn things around all the while. You have probably invested a lot of time and energy into the relationship, are afraid to let go and be lonely, and I'm sure you do love him, but it sounds like he isn't worth the heartache.
I hope things get better.
-z