I understand completely! There were so many warning signs before our marriage that I ignored or didn't really know to be scared of. But, I can't regret my kids, so some good came out of it and I am a much, much stronger person now, so there's that :)
Stay strong! You can do it! Boundaries, Boundaries!
You can tell him you love him, tell him you want him to be okay, encourage a positive relationship with the kids-- and still not go back to him, stay strong in your decisions!