HELP..Im losing my house..and more

I searched and searched the internet in hope that someone can answer my question. I dont require great detail as I am planning on revisiting my lawyer as soon as I can get some funds together.

In brief...my H and and I seperated March 2001. We have 4 children aged 20 (attending University and still living at home), 15, 12 and 11. I stayed in the marital home and last month H pushed for property settlement. I agreed to sign the papers if he would agree to a lump sum payout as advised by my lawyer. In other words, he could forgo the child support for approx the next 7 years if I received 80% of the sale of the house. He agreed. Mind you, in calculating this, he would be much better off in the long term and I could then go about setting up a new life for me and the children.

In my written offer to him, I also offered to pay 50% of any debts that were incurred whilst we were married. He unfortunately got himself into debt and selling the house was his only out option. I would then receive 80% of the remaining amount. Well, I received and email this morning saying that as I was receiving 80% of the house sale price, I would then also have to pay for 80% of all outstanding debts, including the cost of his car that he purchased a few months before we seperated. This amount is about $25,000.

Is this legally correct?....I know each case is different but in theory as I offered to pay for 50% for debts which I wasnt even aware of at the time, am I also bound to pay for 80% of these because I am to receive 80% of the house sale price???

Apologies if this is long or confusing, Im just so upset. All I am trying to achieve is some form of security for my children as his support payments have been so erratic and even non existant since seperation. That is the reason I was trying for a lump sum payment.

Your advice would be greatly appreciated.