Anonymette, welcome to SR. Sorry you had a need to find us here, but you're in the right place for help.
First, I'd suggest you read as much as you can here. I think you'll see yourself in a lot of the stories and you'll realize you are absolutely not alone w/your problems. Make sure not to miss the stickies at the top of the page. Here's a thread from there that you may find especially useful:
http://www.soberrecovery.com/forums/...l-problem.html
It sounds as if you've already had a fair amount of experience w/the repeated broken promises and with the failure of your attempts to moderate his using. Sadly, you simply can't influence his behavior regarding his addiction. Alanon has a saying about the 3 C's: You didn't Cause his addiction, you can't Control it and you can't Cure it. Your attempts at setting budgets and so on are doomed to failure.
Thank heavens you realize that getting married won't solve his problem--remain strong and don't give in to some rosy dream of the future. You've already seen how easily promises to "behave" if only you'd "trust" him go down the drain. This won't change w/marriage.
Looking into Alanon would be a great source of f2f support and education. Attend a few meetings if you possibly can. The more you can educate yourself about addiction, the better able you will be to make decisions about your future w/this guy.
Wishing you strength and clarity.