Definately check out Al-anon because although he broke off the engagement, something tells me he will be back wanting the relationship. It is kind of how many alcoholic bf's are. Not sure why. Maybe because they figure out soon enough that it takes a very patient and understanding person to put up with the craziness that surrounds loving an alcoholic.
I'm sorry he won't stick with recovery but what you did or didn't do has no bearing on why he is drinking or not taking recovery seriously. Relationships all have their ups and downs; unfortunately alcoholics cope with those ups and downs with alcohol while the rest of us don't.
I am a pretty supportive and understanding gf, I am also work with mom's who have substance abuse issues but my RABF still relapsed. He didn't manage his recovery well, stopped going to meetings, etc and thats usually what happens, they take a drink.
It is very tough to love these guys. You see the good in them and you also see the pain they put themselves through but it really is their journey to go on. They have to find their way. For some it takes several attempts to get it right. Regardless, it can be draining so take care of yourself, esp now. You may find al-anon helpful and definately post to us!