please consider not getting married. this guy is hugely troubled. you don't even know him, really. and what outtolunch said about the three day binge is most likely true.
i'm really sorry for all of the crap that you've experienced with this. i hope you find a way to heal. i hope you find a way to be focused on yourself, and your own well being. he will get through with or without you and he's already proven that you being there is not going to stop him from using and doing whatever else. so just take care of yourself. your life could be much more than this.
love is wasted on someone who is too sick to care for themselves, who tells lies, who manipulates, etc. he has so much growing to do and there are no guarantee he'll do it. but pretty much everyone here can guarantee that you will experience pain in addition to what you've felt already.
just some things to think about.