I'm sorry this is happening. In my marriage and any other relationship we might open to, we have always said our children are our primary relationship. So I understand his desire to be in their lives more.
But, as a product of parents who SHOULD have divorced, I can't understand staying together for the kids. Unless they can truly reconcile and they really want to be with eachother, a healthy divorce IMO is better on the children than a consistently unhealthy marriage. And he can remain involved in their lives as long as he's willing to put in the time and effort, with or without reconciling.
I'd rather be hated for who I am than loved for who I am not.