Infelicity
This relationship is well and truly over now because his relationship is with alcohol and not you.
What do you get out of this relationship now?. What is in this still for you because its another crap relationship you are now in and now yet another you will have to extricate yourself from.
Love your own self for a change OP, your ex did not and now this man does not either. His primary relationship is with alcohol and not you. He loves the drink more than you even if you do figure on his priority list which you do not. He like many alcoholics as well is in denial of his drink problem. Your words are white noise to him and he does not want to know.
Are you codependent in relationships?. You sound it absolutely which made it also for this bloke to target you now. Infact you were targeted anyway by him. Your ex was also abusive and this man is no better honestly either for you or your children. Was there much of a gap between your marriage ending and this man now?. I think you were targeted when you were really vulnerable and you remain so now. DO not continue to sacrifice your own self and that of your kids on the altar of his alcoholism.
My guess too is that you did not get enough or adequate support after leaving your abusive marriage and this made you even more vulnerable to the approaches from this alcoholic. You are not valueless but between them your ex and this man have made you feel this way. They are the ones who are not worth it here and you cannot help anyone like your current man now. He does not want your help or support; he just wants you around so you can further enable him and his associated drinking. You are also playing out roles associated to his alcoholism and your kids are picking up on all this as well. Even your mother enables him and you certainly cannot leave your kids in his so called "care" any longer. You are no family unit and what you describe is utterly awful for your children to be witness to.
He will break more than your heart if you remain with him; he will break you utterly and take your children down with him into his pit. Surely they deserve a better role model too.
What do you want your children to remember about their childhoods, surely not this. What sort of a stepfather figure is he to these children anyway?. They certainly do not need or warrant an alcoholic in their lives and nor do you; this is yet another poor and abusive male role model they have been introduced to.
You really do need to contact Womens Aid and enrol yourself onto their Freedom Programme. It is for those who have been previously abused. Your ex messed with your head and boundaries and as a result you've also let this drunk into your lives now.
Longer term you need to look at exactly why these two men were chosen by you at all, you should look at counselling and unravel all this properly. What did you learn about relationships when you were growing up, from the briefest of snapshots of your mother it may well be that she also taught you a lot of crap about relationships when you were growing up.
YY to Al-anon, you really do need to go to those meetings and start further educating yourself about alcoholism. And no you cannot protect your children from the realities of his drink problem either.
Your mother here is not worth paying attention to (did she happen to like your ex as well and/or tell you how good he was with them?). Her words are meaningless.