How can you identify if someone is alcoholic or in danger of becoming one?

[mindy]

Hi, I'm new.
I'm not entirely sure how you can tell if someone is an alcoholic or rather if they are perhaps developing an alcohol problem and could be in danger of becoming an alcoholic or becoming a problem drinker. Can someone please offer some advice? Are there any behaviours which separate these?
My boyfriend told me he used to be heavily addicted to skunk (strong cannabis)and he has quit since we got together because he was worried about it, but without any help. I've noticed increasingly that he is getting extremely drunk several nights a week with colleagues (ie: can't find keys to get in door, can't speak, staggering etc) and on the nights he doesn't get hammered he drinks about 3 beers in front of the TV.
Sometimes he goes for a few nights without drinking anything at all. Sometimes he drinks when no-one else who is out with us is drinking at all which is a bit socially awkward, or sometimes when we are in a pub and everyone is drinking but he orders double what everyone else does.
The thing is he doesn't drink in the day time as far as I know, unless we go for a picnic at the weekend or something, but he doesn't get smashed in the day time.
Just for a bit of context, I'm a typical 20-something girl, who binge drinks about once a month or two (not good, I know!) but only has one or two drinks in the pub on a Friday night, not every week either - so I don't mind other people drinking at all. I'm just concerned that maybe he has an "addictive personality" and could be developing a drink problem. His brother has said the same to me but I find it hard to discuss it with any of my friends because it seems like a private issue.
BTW I'm happy not to drink around him ever if I need to. What do you think though? Does he have a problem or is he in danger perhaps of getting one?
I'm just confused because he doesn't get hammered every night and like I said, not in the day time, so it doesn't seem to fit the usual idea of an alcohol problem. Am I being naive or even overly-concerned?
Any advice gratefully accepted cos I'm not sure what to do. He admitted he's worried about his drinking too but has failed to do anything about it to tone it down despite several promises.