You should absolutely take some time for yourself. If you are healthier and happier, it will rub off on your children. I am familiar with the guilt. It was like I wanted to make up for all the time they didn't have either parent present in a healthy way. Can't be done. I eventually signed up for a college class one night a week. My kids were fine with it and even encouraged me to go when I didn't feel like it.
The other thing you may want to consider is getting out of his relationship with the kids all together. Suggesting he do this or that with them only sets them (and you) up for disappointment. Let him figure out how to connect with his kids, or not. It's his relationship with them, you cannot manage it for him. You cannot prevent them from being disappointed in him. You can only be there and validate their feelings.
When I spoke of projecting your emotions onto them, I was speaking about your anger and disappointment when he lets them down. You are going to have feelings about what he does with regard to them, but your feelings about it are yours. They have their own feelings about it, which may or may not be the same as yours. What you can do is help them to express and work through their feelings without assuming you know how they feel just because you feel a particular way about it. I don't know if that makes sense. It's hard to express.
L