Wanttobehappy...I understand the desire to give him as many chances as possible. I understand the desire to have an "intact" traditional two-parent home. I felt the same way while married to my ex-husband.
As for ultimatums, I've found they never really work, because the goal of an ultimatum is to manipulate someone into doing something you want them to, whether it's for their own good or not.
Instead, I would highly recommend you reflect on your own boundaries in this current situation...what are you willing to live with? What aren't you willing to live with? What will you do if you find yourself faced with things you don't want to live with? It's really important that you figure out these boundaries and then enforce them, not with a goal to punish/influence/change your partner, but for yourself. And obviously, your partner treats you the way you let him treat you...
As for his promises...well, those are just words. Words don't mean jack. Actions are what speak. I suggest you stop listening to his words and start looking at his actions.