Hi! Welcome to SR.
It sounds like your boyfriend is an addict and unfortunately you have become his enabler. Everytime you say "ok, just one more time" or yes to drinking at this party but no at this event. You are enabling him. Right now he can say look YOU said I could. YOU gave me permission. He doesnt have to be responsible for any of it. And if you start to waiver he just has to start making all those promises you so desperately want to hear and he reels you right back in.
Its said often here and speaking as a recovering alcoholic I can promis you its the truth:
You didnt cause it, you cant control it, and you certainly cant cure it.