This sounds so sad. I sure would like you to re-read your post again but this time pretend someone else wrote it? What would you tell them to do? Notice you said him and his wife is jerks? He is not your husband no more but he will always be a man you had children with.
His wife nor you can change that. What you can do is ignore the past relationship and find a new one? If its ignore him, do that? Your children are now adults and you have grandchildren who paying a proce of not having you because of you and his past troubles? How unfair of all of you to do that to them?
Does your daughter have a point about you not being happy? She is not handling it well getting the message across but is she right?
What are you giving up that is the worst? The house?, horse? dog? money? children?, grandchildren? I dare say your happiness! You'd be happy if you could have a healthy relationship with your children and Grandchildren. No house, apartment or living space would change that? I'd love to see you come back in here, we can help you.
What you give up that hurts you the worst is part of yourself. He still has power. You let him still have that power even more gained through him having another wife? Come on?
Let yourself heal now, take ahold of whatever power you can find inside of yourself, try to stop letting what happened then control what you could have now?
One hour of happiness with them grandchildren will pay off.
One day of no talk of him and sharing just routine events with your daughters will give you so much pleasure and when you lay down to go to sleep that nigh, won't it be nice if he aint there no more? I think he is still hurting you. Maybe it is time you let him go and take your heart back?