Dear @Anastasia
Firstly, what you have shared is not too muh info for me and hasn't bought me down. I'm care about you and worried that you are being too hard on yourself. There's no such thing as a perfect parent, or the perfect child.
Being a single Mum, bringing up boys in particular must be so challenging. But you did the right thing by leaving a toxic relationship, so you and your boys would have a better life.
It's never too late to introduce new boundaries for your son's, but I'm sure it will be difficult. Is this something you can speak to your therapist about, in regards to getting some advice. I don't have kids, so can't offer any advice there, I'm sorry.
I recall you saying previously that usually when your son comes back from his father's, it usually ends up in a hospital admission. But, you're saying he's going ok (just won't get out of bed at the moment), so that's good that he isn't as bad as in the past.
Your other son may be feeling deflated about losing his job due to covid. When I was made redundant, it broke my heart, hit my confidence and I didn't have much motivation to start looking for work again for a little while. He may have a mindset that 'I won't get another job, so why bother trying?' Have you spoken to him about not looking for work yet, to find out if there's some underlying fear, and not just laziness.
I feel it would benefit you to try and get to the office a little more often than you do. Is there the chance to WFH in the mornings, and go into the office after lunch for example?, before committing to being in the office for 3 out of 5. You're extremely lucky to have such a supportive boss.
Don't ever shut up - keep posting, I enjoy chatting with you. Not sure I offer the best advice, but I'm always here to listen. 
L xx