I think the problem is that to you, this is a long day, but to many of us, it appears more than reasonable. Yes, we appreciate that you find it difficult, having gone from your DH being around a lot more, to the current situation, but really, for an awful lot of people on here, they would be quite envious of the fact that your DH is around as much as he is! For many people whose OPs commute, especially into London, they can be out of the house before the rest of the family are even awake in the mornings and not back until all the children, and occasionally the other partner, are all in bed! Yes, it is a pain and yes, in a perfect world it wouldn't happen. But it does. So, unless your DH is in a position to change jobs ( and assuming he even wants to),all you can do for the time being is to support him and change your own reaction to a situation that you cannot change.
I think anybody who works, is likely to come home in a mood at times, that's the way it is. You need to decide whether you deal with it by giving him space to chill, or by talking it through with him, calmly, or by giving him more grief over something he probably has little control over. The job market is very difficult at the moment, so he probably feels he can't talk to his boss at the moment because maybe his boss is the sort that would kick him out and get somebody else in his place. Do you really want to live on benefits? That's not being spineless, it's being prepared to be treated like shit because he feels a responsibility to you and your children, to put food on the table and keep a roof over your heads. Actually, I think it shows a real courage, to get up and go to work daily knowing you will be treated like that, but putting your families needs above your own wants.
I don't think it is unreasonable to want him home at 6pm, but I do think it is unreasonable to expect it.I would love my Dh to be home for 6pm. But it just ain't gonna happen. He officially finishes work at 5, but is frequently there till 6.30 or 7 pm. No paid overtime either, so not even the compensation of a bigger pay packet each month. But he feels he has to do it because his industry, and his office in particular, is very vulnerable at the moment and he doesn't want to do anything that will raise his head above the parapet so to speak. Neither of us like it, but we both need to stay in work to pay our bills.
I don't know how old your kids are, but I am guessing they are not that old. Children, IME, do have a tendency to ask where the other parent is. Mine always did. If DH was out they wanted him, if I was out they wanted me. I assume DH works nearby. Could you have an agreement that if he is going to be later than 7pm, he calls you by a certain time? Otherwise you just tell your children what time he will be home. Maybe you could tie it in with teaching them to tell the time? Then give them something to do that will last until that time, even if its just tidying their toys before daddy gets home.
You are not destined fopr a single life, though if you are at home all day it can feel like it. If you have no luck with a job for yourself, could you do some voluntary work? Or a college course to make you more employable? (not meaning to offend, but if nothing else it would get you out of the house and meeting other people regularly) I started to hepl at playgroup when mine were little and it has led me both to some good, lasting friendships and into the most wonderful job.
And it will get better.