Credit Cards ...

My husband and I were trying to come to a separation agreement on our own but he has suddenly stopped all communication. All of our credit card debt (32k) is in my name as the primary and him as an authorized user. Since our house is underwater and he wants to keep it, he originally agreed to pay all the credit card debt if I would walk away from the house. I was advised this might be a good deal for me, so told him when everything else was agreed upon, that would probably be acceptable. Now he has changed his mind and wants me to take on 10k of credit card debt and give him the house. BUT he also wants me to continue to contribute $850 per month to the joint bank account for 5 mos so that he can "get on his feet." I have already given him almost $2k since I caught him cheating and left almost 2 mos ago. He is now in the marital home with his new girlfriend (yes, it only took about 2 weeks for her to move in). We are not legally separated, because he won't come to any sort of agreement with me. He has gotten most of the household items already. The only assets we had were his 401k, which he cashed in and gave me half of and a motorcycle he sold and also gave me half of. I am living with my mother, have bills of my own and need to save to get on my feet again. I guess my question is, how am I to be guaranteed he will pay credit card debt once/if we reach that agreement? The creditors will only hold me responsible if he defaults. I know I can take him to court if he doesn't meet our agreement but by that time, I guess I could be in financial ruin. He says he will not agree to take out a personal loan and pay in one lump sum.