I'm sorry, I did read that you had figured that out after you had already started dating him...
It probably seemed like an odd question, but there is a tendency for people who have grown up in dysfunctional homes to be attracted to dysfunctional people, even if they don't seem that way when we meet them (I'm not trying to say that your boyfriend is dysfunctional, maybe he has stopped drinking, etc.)...
But, in the case of someone who grew up in a dysfunctional household, it's almost like our senses and instincts all have their wires crossed, so to speak. We tend to be attracted to people who are/will become alcoholics or be emotionally unavailable, abusive, etc., rather than being attracted to healthy people who don't have those issues to deal with.
I don't know if that is the case for you or not, since I don't know much about your history. But it is a common denominator for people who have grown up in alcoholic/dysfunctional homes. It's up to you to decide whether this sort of thing is a trend or not.