Anonymous wrote:"he has massive debt..." Be sure to know how much of that debt you are on the hook for and how much of it can come out of your combined assets.
+1 I'd start there, OP. Unfortunately due to his childish "what's mine is mine" attitude, he has no idea, or just does not care, that the deal with debts in a marriage is not "what's mine is mine" but instead, "what's mine is ours." I'd sit down -- you likely will have to do it solo; do you have access to his financial info, what he has in his own accounts, what his debt info is??-- and create a document listing every single penny you both have, separately and jointly, including expenses etc. etc. See how bad the financial stuff is or isn't. The hard part is, if he has credit cards or other things you don't know exist. You might even need the help of an accountant (forensic accountant? I don't know if that's quite what they do). Once you know the numbers, you can take them to someone for advice about what you, yourself, are on the hook for, as PP says.
Any chance that if he's threatened with divorce, your DH might agree to a financial revamp, selling some of his toys, etc.? Would you trust him if he did so, or do you believe he would hide expenditures and debts even if he agreed to change things?
What is the plan for the kids' college funds and your own retirements, plus a buffer for emergencies? Is that all coming from you, OP?
Got to add, I"m so sorry for the situation. Do not let the mean-spirited PPs who play the "this is who you married" card get to you at all. People cover during dating and early marriage and I bet he did just that.