I have been reminded here of a (fairly outing) incident some years ago. I was at a social event for a club (think hobby/sports) I hadn't been doing for long - and was there with two friends. I was staying with one, as lived out of the city at the time.
Another girl (who we didn't know well) got VERY drunk. When we were leaving, she was alone with some strange guys, so made her get in a taxi with us. We couldn't get a home address out of her, so ended up taking her back with us, and putting her on a blow up bed in the lounge.
In the morning, she had disappeared, having also left the flat door slightly open, worryingly. I thought I'd heard a door at about 8am, but had thought it was the bathroom - I suspect it was her leaving. She had also wet the bed (and had slept in her clothes.... so went home in pissy jeans.)
We didn't have a number for her, so had to wait until the usual meet up on a Monday night, at which point she said she wasn't sure where she was when she woke up, so she just left! However, it turned out she had a real drink problem, and this wasn't unusual for her... she had actually gone out for a boozy brunch on the Sunday morning, straight from leaving us (still in the pissy jeans.)
So, I suppose it's worth asking yourself if he has this level of drink problem......