As soon as they even sniff you growing a backbone, the manipulation and empty promises flow like crazy. PLEASE be ready for it. IF you've never seen him cry, he'll cry. IF he's never made an effort or hasn't for awhile, a fancy date will be planned and maybe even a special gift. He will give you just enough to make you think he's capable of being who you WANT HIM TO BE but NOT who he truly is.
I don't mean to be so harsh but if I can help anyone based on my own experience, it makes me feel like I didn't suffer for nothing.
Also, please share what's going on fully with your mom and other people who can support you through this, beyond this forum. We hide so much out of paralyzing fear, embarrassment, shame, etc. For me, once I finally talked about it, I was able to truly accept just how bad it was, and figure out what do to next. You will need your mom and others to support you and encourage, and re-encourage, you to move forward.
Marriage and babies with this person is NOT a good idea. If he can't be good to himself or you, he will not be able to be there for a child. And I can tell you first hand, divorcing an alcoholic is the WORST!!!