B.F.
There is nothing in this marriage that would change for the better by divorcing. He would just be leaving his kids with a single mom who would be more overwhelmed and more angry. The only thing he would get out of it is, out. Time for him to go to counseling. Get ideas on how to deal with her reactions and protect the kids. If he invests in them instead of runs away, there is a chance for things to change for the better. Maybe if she sees him consistently going to counseling and how he grows and changes, she will stick with a counselor and get better. Maybe his contribution to her problems (nobody is perfect) could be lessened and she would be less overwhelmed.
He doesn't want to? Well, sorry. He married her. He has 2 kids and they deserve 2 parents. He doesn't want to live with her but he would "never take them away"? Kiind of sounds like is ok with her care of them. I vote he works from there and not chew off his leg to get out.