As long as he's doing 4 at his sister's and 4 at the house he's not spending money on rent, which is probably good for your finances. I'd take advantage of the freedom afforded by him being there 4 days a week to spend the night at a girlfriend's, or go out late, or spend the night visiting your dad. Or go out of town for a few days! Let him wonder about your busy interesting life.
As for his complaints about you - you know most of them are not based in reality. And how much of the debt was really due to your cancer versus to his spending on toys I'd like to know? (Btw my boyfriend has lung cancer, it's an f-ing full time job going through cancer treatment, so don't beat yourself up about it.)
And btw - although the emphasis here is usually on how to repair the marriage, I just want you to know that it is also OK to say "he betrayed me and broke his vows and I don't feel obligated anymore." Everyone has to decide for themselves whether the marriage is worth repairing and once the partner has broken their vows I don't feel you have to be obligated to stay in the marriage unless YOU want to and think there is hope. Sometimes the flaws in the marriage that we were putting up with for the sake of our marriage vows become more visible with a little space. And sometimes how a partner responds during a health crisis is very telling . (I have a friend who just moved out from her long-time partner. She had ovarian cancer last year and he didn't show up to pick her up after surgery until hours later! EXTREMELY unsupportive throughout her treatment so now that she's better, she's out of there.
