Can I ask how other people deal with snappy/moody partners/husbands?
I like to think I would dump them nowadays. Had enough of that from my dad growing up.
Also it is very damaging to children. I've been left with lifelong anxiety from the walking on eggshells, and have never really been able to work.
I’m a good person and the result is we’ve ended up in a situation where he lives like a single man with the benefits of having a wife but never having to do anything he doesn’t want to do.
So his moods and the threat of his moods he uses to control what happens, so everything is as he likes it. 
It’s too late for me to find that now
Of course it isn't. xxx
He has no regard for my feelings at all. He just doesn’t care if he upsets me. It’s that simple. I emailed and wrote down how I felt. He either ignores or writes back a load of vitriol. He never just backs down and says sorry for upsetting you
He's horrible OP.

He often denies what happened or just turns it back on me
This is classic in an abuser.
He withdraws attention or any of his company.
Have you any friends or family you could see for company? He's not a nice man to be with and you never know when his 'company' is going to turn nasty. And he doesn't deserve your company.
I just don’t know where I’m going wrong.
That's because you're not doing anything wrong- he is.
There's no point constantly hoping to find some magic way to get him to be nice to you. If he does for a bit it's just a tactic to stop you thinking of leaving.
There's no way you can fix this because it's how he is.
If you leave then at least 50% of the time (probably far more as hopefully he won't want that much work) the kids can be free of him and relax, and not be learning from his antisocial behaviour. And you won't have to put up with him any more. xx