There was an n in my life, who has a relationship with my children, but no longer with me. I did as Bunny suggests and basically told them (my kids) that the problems were between the adults, and that I didn't want them to worry about it. Also, that they may feel angry, upset, etc, about the adults not getting along and that that was ok and I would do all I could to help them through it. The children accepted this.
Years later, they are still hoping to see a reunification and I find it's difficult for me to explain what behaviours caused the disruptions, even though they are much older now, because I don't want to interfere in their relationship with the n person (although deep down inside I would like nothing better than to end those relationships-I do know that that is not up to me). At the same time, I see my children's confusion and I want to help them understand. It's hard to explain without explaining. So now I'm giving simple explanations when they are requested. No more covering up or dancing around the facts.
If I could do it over again, I would be more factual, giving some simple information about actual causes/behaviours, right from the beginning, and seek expert counselling.
Since your H lives elsewhere, now is as good a time as any to secure your financial situation, regardless of what he is telling you he will do. Take the necessary steps to be sure you won't need his generosity, which can vanish on a whim and to protect your assets for yourself and your children.
Best of luck to you! Take care of you too, ok?
s