I can relate to this, to an extent. I had a "thing" with a man I met through work...was actually a client of ours. Huge no-no in my line of work. It never went beyond anything physical, but we both were/are in love with each other. He's even slipped up and said it a few times, then tried to cover it up, and his covers were so lame it was actually funny. We're both well aware that we are not meant to be together, and that all of the circumstances are totally against us. He was married, and has a young son, and is in the middle of a very nasty custody battle. Which he's pretty obsessed with. (And I've blatantly told him that before). He talks about his ex wife, about his son, about all of his legal drama....CONSTANTLY. Constantly, constantly, constantly. He puts it off as he's just a parent who cares about his son. I don't know if he's in denial, or just plain doesn't hear himself, but he does not seem to see that he's also obsessed with his ex wife. Way beyond the issues and drama with his son. He's WAY too concerned about her in things that have nothing to do with his son. As our physical relationship has died down over the past few months, I still have to talk to him (almost daily) for work, and I've found myself getting SO angry at him. I've said horribly nasty things to him that not only are totally inappropriate at work, but are also totally uncharacteristic of me. I've never spoken to someone like this before, and I've never been so mad at someone before, for absolutely no reason. Other than I was having to listen to the drama again for the millionth time. One day I finally realized, I was so mad at him because I knew he was never going to love me or devote this kind of attention to me, the way he does about his ex wife. The woman he claims he wouldn't p*** on if she were on fire, still takes up so much of his time and energy and attention, and I was jealous because I knew I was never going to get that from him. That's where my anger came from.
Realizing and understanding where this rage at him comes from has helped me a lot in dealing with him, both professionally and otherwise. He calls us "friends" all the time, but I don't consider him a friend. Mostly because it is 99.9% always about him, and I don't think he could even tell me the most basic thing going on in my life. And I'm moving on with time. I'm no longer at his beck and call, when he says jump I no longer say how hi. It's gotten a lot easier. I had some bad drinking nights because of him (but I also had some bad drinking nights because I got a paper cut - I didn't need a real reason). I know this isn't the exact same story, but I do understand how you feel and I can tell you it does get better. Like anything, it just takes time.
I would not use his vacation as an excuse to drink. It's just that - an excuse. Next week, there will just be something else to "get through" with drinking. Take some time for yourself away from this man, and it will get easier.