OP, you say 'If I could truly believe that he knows what he’s doing and how badly he’s affecting me, I’d find it easier. But I just can’t or won’t believe that he could be that cruel.' What is it with women that we simply refuse to believe what's happening in front of our eyes? There has been another thread running for quite some time now, posted by 'Devoed', her husband accused her of an affair, and ultimately deliberately got HER arrested, and turned out of the home that SHE paid for, together with their children. She has been exactly like you for months, even after he had her arrested, she was still trying to understand why he would do something so evil, but he DID!! That is the man that he is, and your husband has been showing you for a long time who he is, but you won't make yourself believe that either. I simply don't understand, and feel that you REALLY DO need to leave him.
You say that your kids do more than they should around the place already, although I can't see how that can be the case, if you have a cleaner. What exactly do they do around the place, that stops THEM from taking care of their own ponies? In my opinion, if kids want animals, then naturally the care falls to the parents while they're small, but you say that yours are teens and tweens, surely the teens can supervise the others (how many do you have, and how many ponies?) to do at least some of the work involved, and if not, why not?
You seem to think that the world will fall apart if you take time out, and go away, but if you were to die, or have an illness which meant that you literally COULDN'T do all that you do, then your husband would HAVE TO sort everything out, whether he wants to or not.
Don't get me wrong, I totally understand that you're concerned for your children above everything else, but if you end up in hospital with a complete physical and mental breakdown, they will suffer anyway. I don't know the sort of person you are, but if it got to the point where it was all too much, and you decided to take your own life, or simply walk away, as many people do every single year, they would also suffer. At the end of the day, your HUSBAND has caused all of this, NOT you! The only mistakes you've made, are marrying him in the first place, and not leaving him sooner. I know, having been through divorce myself, how much it can affect children, but at the end of the day, I bet there are very few kids who would rather see their Mother go through hell, and live in a miserable household, where when their Father is at home there are frequent arguments, and when he's not, their Mum is stressed beyond belief, rather than be part of a broken but ultimately happy home.
You CAN get through this OP, but you MUST leave him, and sooner rather than later, if not for yourself, for your children, as living this life WILL be affecting them, whether you think so or not.