I am so sorry that you are going through this mckell. You seem to have your head on straight, just a bit reluctant to take that last step. Your relationships with your step childrens should not change, they are already familiar with how their father is.

If you are in the states, make an appointment with a divorce lawyer, the first session is usually free. Ask about custody, support etc. I find it hard to believe (but not totally, life is stranger than fiction) that with children you'd have to support him as well.

Good luck.