I have felt very similar in the past, generally during maternity leave.
In my case, 80% of the problem was the uncertainty. My whole life was chaotic (newborn twins are not predictable!) and then DH never arrived home at a consistent time either. My DH has a long commute, so I asked him to text when he got on the train, or to text at 7 if he wasn't on the train by then. He sometimes managed it, and on those days I felt so much less abandoned - he'd remembered so was thinking of us, and I could make a vague plan for the evening.
Having done the pressured job plus long commute myself, I understand why he finds it hard to plan when he'll be home. To be home before 8pm he needs to leave the office shortly after 6pm, and in many London offices things are still in full swing at 6pm. So you get distracted and it's too late to catch the train, so you have 30 more mins at work. If you get distracted at the wrong moment again then it's another 30 mins .... And it's easy to get distracted when the office is still very much working and not winding down.
For us, the answer was for me to not expect him home at any particular time and my to plan on his help. If he turns up and chips in then that's great, if not then I will manage. During the week he just goes to work and takes care of himself, and I manage the home/family. Sound a bit 1950's, but it's what works for us (and I don't feel any obligation to cook for him or wash his clothes etc - if I do then it's a bonus, if not then he gets on with it). We've just decided that Monday - Friday he works hard to advance his career (which also involves social stuff, though I don't ask for details often as I get envious!) while I am responsible for the home stuff. If I want to do social stuff during the week then I ask him to be home by X time and he does his best to reschedule meetings etc to be there or tells me up front that he can't do it. At the weekend we divide stuff differently in a way that works for us.
Lots of waffle, sorry. I guess what I'm trying to say is that there may just be too much in your combined lives to enable him to build a career, you to be off work and for him to focus on family stuff every day. If you can discuss it and agree with him where your combined efforts should be spent for the next 6 months (and what the cost/consequences of those decisions might be), then you might stop feeling so resentful because you each understand and agree on the long term goal?