Pull a free credit report on yourself, and find out if the mortgage shows under your name/SSN, and what other marital debts include you.
If you are upside-down (and after 12 years, I bet you're closer to break-even that super-far-underwater?? check zillow.com) . . . I'd be inclined to take his $2k'ish/month, skip making the mortgage payments, and let the house go into default. I'd ESPECIALLY be inclined to do that if you are NOT on the note (and it doesn't show up on your credit reports -- check all 3 bureaus, btw). You could sock away funds, and then eventually reach out to the bank and/or someone who buys it after it foreclosures, and offer to rent back from them, keeping your kids in the same house. If not, you could find other suitable rental home nearby for $1200 - $1500/mo?, trying to keep your son in the same school district, but you would have socked away $1200/mo for 4-12 months (or even longer, if you wanted and were willing to file for BK and/or do other things to contest the foreclosure action).
I know it's all scary stuff, but if the house is NOT in your name, you really may have some good options here, Train. Renting ain't bad (think: NOT YOUR PROBLEM if the a/c stops working, or the roof leaks!), and you could rebuild your own credit in 2-5 years.
