Frog...
I've been in your shoes, girl.
My advice...contact the loss mitigation dept of your mortgage lender and tell them that you cannot pay the increased payment. Tell them you are listing the house. If you want to keep it, they will work with you and if you don't want to keep it, you can almost always sign the deed over to the bank in lieu of foreclosure. Its a hit on your AH's credit but not anything as bad as an actual foreclosure. Banks are usually willing to do this because they don't have to go thru the costly and lengthy process of foreclosure.
What you do next depends, in large part, upon how much equity you have in your home. You won't want to do a deed in lieu if you have equity...but if you don't have any equity...and if you're looking at selling it for less than you owe than a deed in lieu will prevent the bank from coming after you for any shortage on the sale price. (a short sale will do the same thing).
Its always best to contact the loss mitigation dept before doing anything drastic. Find out what your options are before diving into a foreclosure situation. EVen if your AH doesn't care at this point...he might somewhere down the road.
Whatever you do...good luck...