I haven't had that happen to me. However, it doesn't sound very good. It probably isn't so good that he likes to go drinking so much, plus having a girl there that he has been becoming friendly with.
People like to think that plutonic relationships work between men and women--saying "we are just friends", and really many times that doesn't work. The fact that he talks to her everyday isn't so great either. However, I don't know if you guys had any guidelines between the two of you on that subject.
My husband and I have certain guidelines that we follow. We don't develop friendships with people of the opposite sex. We try to be very careful. We set the guidelines up so that we are both happy and feel secure in our relationship. Maybe not everyone has to do that. However, it prevents alot of mistrust and misunderstanding. It builds up our trust.
On the other hand, you don't want to be unduly suspicious either. I think if you were around the two of them, you would be able to tell pretty quickly what kind of relationship they have. Maybe, she is just a pathetic needy person. So maybe try to examine it as best as you can before you approch him about it. If you can bring it up in a way that helps him see your feelings and not think that you are just being crazy jealous.
People think jealousy is always bad, however, on the good side it shows that you care about the person. You sound genuinely concerned. I sure hope the best for you--it has to be hard to see.. :)