I don't want to guess too much about your situation, because I don't want to be alarming when there is no need. I'll tell you what has been my experience with a traveling hubby.
He travels pretty much every week- Mon-Thurs or Friday, then home on weekends. After longer trips he would have a harder time being home. He was used to working all day then going to a quiet hotel room and not being bombarded with kid stuff (and wife stuff!). Simply the awareness of this was enough to help him adjust, and be able to remind himself "oh yeah, I'm home now and stuff needs to happen all evening". No problem.
Little things, like he orders whatever he likes for meals out of town, so he'll be home and ask what's for dinner. I'll tell him and he often said "hmmm, don't know if that sounds good". Really? Then let's eat what YOU cooked. Again, awareness of why this habit started was enough to end it (along with my furious response!).
The drinking. I will say that my husband did say he would sometimes go down to the hotel bar to do some catch up work and have a few beers. I didn't like this for many (probably obvious) reasons. I don't want him to not have any relaxation while gone, but I need him to not be the guy drinking by himself in a hotel bar. So he now tries to schedule more work dinners so that he can be with other people and relax that way. He doesn't drink at home.
I can also tell you that these things seemed amplified when our daughter was younger. Routines and phases change so quickly, he felt like he came home and couldn't do anything right because it wasn't how we were doing things when he left. Not sure how old your kids are, but that was my experience- it got easy when she got older, not so much of the screaming, needy, energy-sucking little kid thing.
Not sure if that perspective helps you or not. I would suggest asking him more questions than telling him things. Ask what it's like being gone for a while and then coming home. He may tell you things that surprise you. Or maybe not, but you can at least acknowledge what he is feeling and let him know that "I get why you feel this way, I also still need you to be plugged in when you are home". And then work on ways to ease him back in. But at the end of the day, he needs to re-involve himself better than he is doing. There is a supportive way to meet this need, but he's just got to do it.
Once you've worked on that, let him know that you are not comfortable with how much he is drinking. Others said it, and it's simple but true- if you have a problem with it, it's a problem.
Good luck.