Yes, it's possible for the drinking to be a deal breaker even though it may not be a serious problem (although people can be alcoholics without getting drunk). I don't know how you can tell if he has a problem or not - the bigger issue is that *you* are concerned with the alcohol intake and he is not. You can both be 'right' about this.

At six months, it seems too early to me to get involved with his parenting decisions. What do you think his reaction would be if you brought up your concerns and observations?