My first thoughts are, if you are able to work and go to Uni, no matter how long it's for, you're still functioning. Just like you've been functioning today replying to posts on MN. That wouldn't have been on my list of to do things if I was as ill as you say.
You mentioned talking to him today, again if you're really ill you would leave that until you feel better.
He's right, there's no one to look after his children, so he has a responsibility there. If you have the flu, you'd be sleeping as much as possible, dosed up with your usual meds and paracetamol/ibropufen. You could have stayed in bed.
Regardless of what he contributes to his ex, it shows he takes his responsibilities seriously, which not all men would/do.
I'm older than you and have serious health issues, if I have a bad day like today, I've slept from last night till past 8pm in lots of pain. I'm an adult and whilst I'll with underlying issues, or a virus, I've never had or expected care from anyone.
Imagine his post on here if he were to post about his situation. I'm guessing if you're that ill, you'd be getting student finance and an array of benefits. Plus you said your children have SN so you'd get money for that too, which puts you in a better position financially than.
I'm sure there must have been a conversation that went like, 'If you go to Uni now you'll get the loan and bursaries, so we'd be better off as a family!' The only down side is ESA obviously is regarded as income as is the student loan when it comes to housing benefit, so you're not entitled to as much housing benefit as you were.
You have to beat in mind that whilst not all MN will know what your doing, there's some out there that will. Apart from you having to pay more rent, you are generally better off with the student finance coming in, forgetting CTC, WTC, CB, ESA, DLA/PIP, if you get the last 3 from being ill.
Due to the condition, OP will have a nice desk, a chair that costs about a £1000, plus computer and printer etc, for being a disabled student. They'll also pay her internet fees. Pay money for books and other consumables.
So realistically it's unlikely that DP will bring in amazing stuff, unless he's classed as a disabled student. Then I'm guessing he might have a lap top instead of desktop to do his work on.
I've volunteered for various charities, dealt with many families, so I know if at all possible, the student payments, roughly £3000/4000 every term are considered a bonus. For a couple it would be £6000/8000 as you'd both be claiming the ADG for each other which is another £2000 each split in 3.
Ok so he didn't wait on you hand and foot today, do you use a w/c to get around? In which case couldn't it have been carried upstairs to help you?
Men seem to be in a lose/lose situation, damned if they do the right thing, damned if they don't. He has children to sustain, it's not there fault that Dad has been coaxed into going to Uni. If their Mum is as bad as OP says, then they need stability.