Gosh, this is one of the most heartbreaking threads I've ever read on Mumsnet.
Your partner has well and truly managed to convince you that he's the victim here, when in reality he is the abuser and you are the victim.
20 episodes in 15 years, with some obviously lasting days, and one lasting months. You've spent so much of your life thinking you're trying to help someone get better, when the reality is that he isn't and he won't, and over time he has made you into a compliant victim of his abuse.
As someone said upthread; he's getting counselling - great. Is it helping - obviously not. 20 episodes in 15 years is at least 15 too many. I can understand that the first one is a surprise and you think it's going to be a one-off, the second one is a challenge, by the third one you see that something is badly wrong, by the fourth you see that he needs to make this right or you leave, the fifth is the last chance 'relapse'.... but after that, it's just the same horrible pattern repeating over and over with no sign of it ending.
His rant to you about how you're the source of his problems should show you he doesn't have true insight into his issues and the counselling has done sweet fuck-all, even if he can 'objectively' see it once he's out of an episode.
There is nothing wrong with the fact that you can't cope with this. Nobody I know could, or should have to.
He says you are the source of all his problems, it's all your fault, you're not good enough, you don't know how to help him... fine. Agree. Accept it. Clearly you can't help him. (The truth is nobody can except himself.) The 'help' that he demands (compliance, quiet, your undivided attention) is utterly unreasonable.
You don't have to pass his test. You don't have to accept the weight of 'being just one more person to abandon him', which he will no doubt throw at you. Just accept the simple truth that you can't help him.
Just like he is the only person who can help himself here, you are the only person who can help yourself here. The only people who can't help themselves are your children, so THAT is who you need to focus on helping.
And you do it by telling your husband that you've thought over what he's said, and you finally accept it. So you're going to move into the new house by yourself with your children, because they need a stable home, he's going to find somewhere else to live, you're going to get divorced and sell the house, and move on with your lives separately. He can find someone else who can fix him, if he really thinks that person exists.
I'm sure that seems horribly hard to you, and no doubt he's been relying on the fact that it's horribly hard to get away with his abuse for years. But it's time to break the pattern. You are the only person who can do it.