Kelli,
Divorce is never easy for anyone, especially given your stroke. I do not envy the challenges.
My parents were divorced when I was 10 and it was devastating but we survived, poorly, though. I never saw my dad for 10 years and soon after he died.
I got divorced after 20 years, before I ever had a stroke, so I can imagine how horrid it is to have both issues.
What I do know is there will always be a lifeline between you and the ex. That is actually a therapeutic term for the situation, because many think divorce is a solution and do not realize it does not end the relationships. I envy that in some ways for you as my ex totally walked away and left me and children behind. Now of course he regrets it but there was never a lifeline and there needs to be one.
It sounds like you both have a good lifeline, but he is taking advantage of it and you do need to speak out, as you stated to ask for what you want and get a working arrangement with the hope that you both can benefit from the relationship. Mostly your son seeing two grownups getting along and able to corporate with each other is so healing for his later life and intimate relationships. You are his role models and your good heart has been doing a good job to maintain a working relationship with ex.
I imagine it might be sad for your heart to see him moving on, if you still have feelings in that way for your ex. I hope for a uplifting future for you soon. For you all. Keep the faith!
ps, maybe he could bring you some great food in for meals as payment and to help with your grocery bill. Just a thought for your life improvement.