You sound lovely op. I can see why you feel as you do and tbh any spare money I would use to get some therapy for yourself as this guilt you’re feeling seems to perhaps be a trauma response.
Your ex is an addict, who isn’t seeking professional help. It is therefore more likely he will fail.
If he attempts suicide, this is on him, not you. Sorry to sound harsh but you cannot put this upon yourself.
Please stop trying to fix him when he isn’t doing everything he can to fix himself.
I understand that you want the best for your children. The best isn’t trying to fix your ex. The best is putting boundaries up.
Do not. Do not. Put your financial future at jeopardy for him. Giving an addict money is too much temptation so trying to be kind to him could spectacularly backfire. How would you feel if he used that money and overdosed?
If he wants to move out, he can get a room in a flat share. Right now that isn’t on the agenda and I can understand why.
If he is able to secure a tenancy on his own (unlikely), he only needs one week’s rent placed in a deposit insurance scheme, which is non refundable.
As for him spending money on your kids, he needs to save up for that. Is he paying rent at home? How much money does he have at the end of the month?
If you want to help him, maybe talk finances through with him and make suggestions on things he can do with the children. That is as far as you should go tbh. Everything else is treating him as a third child.