I'll offer a male perspective on this. Not saying I'd handle this the same way he has, but I do kinda get where he's coming from.
Your husband has already been through a divorce that, by the sound of it, decimated him financially. He has had to fork out an enormous sum of money to buy a house for his ex-wife, and the effects of that on his own financial stability - and his ability to ensure that his kids have a secure financial future - has been profound and long-lasting. He is working very, very hard to recover the situation, so that he has financial security for himself, and can cover university costs for his kids.
That sort of experience stays with someone. Trust me. During my marriage, I supported my ex wife unquestioningly. She never particularly enjoyed work, whereas I worked hard and was successful. So when she chose to go part time before we ever had kids so she could spend more time with her family, I supported her and picked up the slack. When she wanted to give up work altogether, after we had kids, I supported that, because it was right for the kids and right for the woman I loved. When she didn't want to go back to work later, because of mental health issues, I supported that. I'd have loved the opportunities she had, to work less, and spend more time with the kids. But I did my bit and brought the money in, and was a hands-on dad every minute I got. And then when, eventually, after years of abuse and ultimately even violence from her, I left her - well, at that point, every one of those supportive decisions I'd made for her justified why she had to take an enormous settlement (because she would never earn much herself). She took every penny of equity that had built up during the entire marriage. And, even now, she barely makes any contribution to the costs of the kids, despite us having them 50/50. She remarried within months, and now all that equity she got is at risk of never being passed on to our children - if they get divorced, or if she pre-deceases her husband, that money may never reach the kids. So I'm feeling the pressure - my costs are through the roof, and I need to re-establish a solid financial future for my kids. And I'm doing it. But I'm doing it alone. The specifics are a little different to your husband, but I tell you that, because it may help you to understand that once someone has been taken to the cleaners like that, they often resolve to never, ever be in that position again. I know I have. My finances can't take another hit like that, and neither can my kids' futures. They come first. I'm sure it's the same for your husband.
He is still dealing with the fallout from his last marriage. Before you and he married, you agreed financial arrangements to last through until the kids were 18. Those arrangements make a lot of sense - they ensured that you were both able to provide for your respective kids, without the other putting that at risk again.
But now things have changed. That deal you made isn't holding any more. You chose to give up work, and have stayed out of work for 18 months. You're planning to stay out of work for another 6 months, and the way you talk about opportunities makes it clear that you will only go back to something that suits you. Having been out of work for such a long time, he must realise that the chances of you going back to the kind of role you had before are diminishing by the day. Skills fall out of date. It's asking an employer to take a major gamble on somebody who has taken such a long time out with mental health issues. You dont seem to have set out a clear plan for a return to work and to financial self-sufficiency. I appreciate that you've done a yoga course, and I can see why you'd suggest that shows you're not just doing nothing. But, to him, that could easily look like something that not only distracts you from getting back to where you were, but is actively moving you in a different direction, away from financial self-sufficiency.
I understand that you've been ill (which is why I hope I wouldn't handle this in quite the same way as he has). But, from where he is sitting, history is dangerously close to repeating itself. This impressive, self-sufficient, driven woman that he fell for, and made an agreement with that protected his kids, has shifted the goalposts. For understandable reasons. But reasons that still put everything he's working for at risk - his own financial future, and that of his kids. For a man who has been through a bruising divorce and been financially decimated previously, that's terrifying.
If you're asking him to support you, the very least you need to do is (a) set out a plan for getting yourself back to financial security, because without that then promises to repay later aren't worth much; and (b) really talk with him in a way that recognises the worries he will have, and figures out a way to ensure that he's provided for his kids first (before providing for you).
That probably sounds a bit harsh (I await a ritualistic flaming from Mumsnet users). I don't mean it to - I really do understand that you're not well, and that can happen to anyone. But I totally get why he's staring down the business end of every fear he will have about the future following his divorce. And my empathy for that is why I will probably never re-marry - and certainly not until my kids are adults!