HH, one thing that I did that I highly recommend in your sitch is take a week off. I went camping, both on a beach and in the mountains and didn't talk to W for 2 weeks. You could also go visit some far-flung friend or relative or something.
If you do, you'll force W to see what it will be like to be single mom without you around. She'll have to be responsible. It will be hard on your kids, but they'll be OK.
You can simply tell her that you are completely stressed out and need a break (which is no doubt true). When I did it, it was a tremendous help with detachment.
Just an idea that worked for me ... and I've seen a lot of similarity between us.
The LORD is near to all who call on him, to all who call on him in truth." (Psalm 145:18)