I should have paid attention when my xa showed up for our first date smashed. I should have listened when his roommates said it was normal for him to just go and pass out when he'd had enough beer (usually a 12 pack). I should have listened when I learned he came to CA to get away from drug addiction in another state.
I am not saying that your situation is the same. But, if you feel like he is drinking a little more than other people you know or more than you feel comfortable with, you should listen to your intuition.