I'm sorry to hear your H couldn't find the courage to continue. That sucks!
In regard to your legal questions it is best to get advice from a professional as laws vary from state to state. Lots of similarity, but different in some ways. As you negotiate your legal options, keep your childrens best interest in mind. You're their rock, you've stood for family all along.
If you are truely seeking a D, you are entering a contract. Treat it as such. You are negotiating on something that can and will affect you for at least the next 16 yrs (you have a 2 yr old right?) Typically, most legal and monetary obligations end when the children turn 18. Educate yourself, just as you did with infidelity. The more you know, the better you will understand the process and eventual outcome.
I hope you are holding up well, this can be a very trying time.
