I think Quentin did have a serious drinking problem-- not just for fun, but actually an alcoholic. There were several occasions where he was clearly drinking to alleviate anxiety/fear or escape from the terrible reality. That's not just over indulgence
People do that a lot without being alcoholics. It may be the most important use alcohol has, despite the drawbacks and damage it can do. Not very PC but true. It wasn't exactly as if there was a more practical and less toxic alternative, for Quentin. One of the most interesting things about a werewolf story is the seeming absolute lack of hope. On the other hand, drinking "just for fun", that's not any less harmful, when overdone.