Would you separate in these circumstances

I think this is really excellent advice.
Divorce is hard, and especially for the children. I feel tremendous guilt over the breakdown of my marriage and what subsequently happened to my children. I'm in my 60s now, and it seems never ending..

That sounds hard OP. Have you tried being explicit in asking him what to do? I know you shouldn’t HAVE to, he’s an adult who should just know that he should be doing his fair share, but if he is otherwise a good man it’s possible that it’s just become the status quo and he doesn’t really know what he’s supposed to be doing. “DH I’m going to get the dinner on can you run round the bathroom while I’m cooking”, “I’m going to get the kids bathed and ready for bed, can you get the uniforms and pack lunches out for tomorrow”. I would try and literally spell it out for him for a few days see if he is actually willing to help and just isn’t sure where to start or if he is infact just a lazy arse who isn’t willing to pull his weight. His responses will be telling.

I wouldn't leave it up to his discretion to decide what "his share" is; even with good intentions on both sides it's pretty common for partners to diverge on (1) what constitutes "good enough" in terms of cleanliness, tidiness, good/nutritious cooking, etc. and (2) how much one partner is contributing (not just how much time they are spending) vs the other on necessary shared responsibilities. If you haven't already, I would try brainstorming together and writing down all of the things each of you are doing that qualify as shared responsibilities, eliminating those that don't need to be done or can be outsourced (chores for children, perhaps having a housekeeper a few times a week), and equitably and realistically splitting up what remains. Consider the time each takes and also how pleasant or unpleasant it is for the doer - and don't forget tasks that aren't cleanly daily, weekly or monthly. Agree not just on who gets what task but when it needs to be done by - and if you give chores to young children decide in advance which adult they go to for help/advice and who's accountable if the chores don't get done. Keep communication open so if someone ends up with too much you can adjust, but only by mutual consent.

I would consider his longer hours when splitting things up, but also take into consideration if either of you have separate time commitments like a long commute, frequently being required to take work home or be on call, caring for extended family, classes or continuing education, etc. The goal should be that you each have roughly the same amount of free time in an average week. Right now it sounds like he thinks you are "in charge" and he will usually only do a task if you assign it to him - that doesn't make sense for adults and isn't fair or reasonable.

If he can't agree to a reasonable split or if he still can't do his share after all of that, then I would be thinking that he believes that his time and his needs and wants are more important than mine, which in turn would make me reconsider remaining in a relationship with him.

I had one like this. Once resentment is there it's hard to mind a way back. It's so relentlessly tedious dealing with these manchild types. I'm a million times happier on my own. It's hard working full time and being a single parent to teens but by God it's a much happier existence

Emotionally, you sound entirely checked out from him. I appreciate what irks you are all of the practical / homely things, but that's just one (not especially big IMO) part of a relationship.

Do you get on great, support each other, have a good physical relationship, have a laugh, raise your children on the same page...?

Because if you do, I'd do what I could to make the relationship work and then farm out whatever else I could i.e. get a cleaner (£40-60 a week could hopefully be found in the budget somewhere), give the older kids a chore chart, automate things like insurance and appointments...

He might not want 50/50 is he’s a lazy sod - and you can’t force him to have it either !

I'd be trying a chores app before splitting. A rota that's never spoken about, where chores are assigned and rotated with reminders popping up daily on his phone. I'd also let him know this whole situation has made you so low, you've given serious consideration to splitting.

I’m going to be harsh here. If he’s been like this for 20 years, you chose to have 4 children relatively recently, especially your youngest, in knowledge that this is what he’s like. I do think there’s some culpability on you then breaking up the family for that reason.

Is there an option to get external help with the house and pay someone to do DIY once a quarter? Split up the daily tasks between you. Four young children is tons of work. Feeding and laundry alone mammoth tasks never mind running the house and keeping up with all the school stuff.

If you can afford it delegate it out.

You are properly in the trenches now. My kids are teens now and it is tons easier and less physically exhausting.

Ugh I was you op, it gives me the heave thinking back to it. Separate, give him 50/50 custody and use your free half of the week to find some joy in your life and have peace while he’s forced to do his sodding job as a parent and adult. He can’t sustain the partner role so cut your losses and see what you can rebuild while you’re young. I’m still single 4 years post divorce and not sure I’d even want another partner. I’m 42 and much much happier. I don’t even have the luxury of a coparent as he’s useless and I’m still happier!

Then that’s different . You’ve fallen into a pattern of being his maid - he seems happy with that . Only you can change it .

I think once simmering resentment creeps into a relationship it’s hard to go back tbh. The more worrying thing is you saying that he really seems to believe he is pulling his weight so he is either deliberately doing this to make you doubt yourself or he is just stupid. I would probably give it one last go of writing down everything each of you has done over a period of a couple of weeks (which will inevitably result in him accusing you of being petty) and using that to start a conversation but I think it’s time to be very clear with a timeframe of how long more you are going to tolerate it. Don’t make idle threats, “if things don’t improve by 1st April I am done with this relationship and we will be looking at making arrangements to live separately”. Personally I would also make it clear that separation doesn’t mean him buggering off and leaving you to it. Good luck.

Im not suggesting this is answer to all your problems but would it be more bearable if you paid for a cleaner? And what happens if you say things like: Can you wash up and clean all the kitchen surfaces tonight its your turn? And are the older two starting to do some chores too?

He's not going to change after all this time is he, especially as you've mentioned divorce before, but not followed through.

The question is whether you can continue to live like this forever? What will that be like when the kids are grown and gone? Will you end up as a seething ball of resentment and regret that you wasted your best years on this manchild who doesn't value you? Is he worth it?

If you’re leaving him because he doesn’t pull his weight - well that’s not going to improve when you’re single ! You’ll still be doing everything alone ! And you can’t force someone to see their kids when you split - I’d he can’t be arsed then there’s nothing you can do about it.

Following, i'm in a very similar dilema so interested to see what others think.

This was my life. It’s horrible. Someone close asked why I hadn’t left as I was so miserable but it didn’t seem like anything catastrophic enough to leave for. I was so wrong. It was death by a thousand paper cuts. I did leave and god I’m so much happier. My children are a million times happier too. I’m not so sad / stressed so I’m more fun to be around and as it’s just me and the kids, we play more which they are thrilled about (instead of me cleaning up after a grown manchild)!

I have no advice but offering a hug and solidarity. I don't think they ever actually change. I was married to a lazy bloke and some how have managed to now live with another one. Will do things if asked but otherwise does nothing much except talk a lot about pushing the lawn mower around. DIY skills of a toddler. Will sit and watch the TV whilst I beaver away. I did find however that sorting the washing and washing only mine had a noticeable impact.