csa and mortgage?

Hi Everyone J I would really appreciate your views on the following.

Just under 6 years ago my partner and I got together (never married). We had our own homes and after a while I moved into hers and we had a baby. We then before the baby was a year old as we wanted a bigger place sold them to buy a place together. She made £60,000 on the sale and put it as the deposit for our new home but I had no equity. We are tenants in common and she had a document made up protecting her share of the investment she made. The house was bought for £115,000 so we have a £55,000 mortgage. Due to the economy here is now negative equity of about £20,000 - £30-000.
She gave up work to bring up the baby when she was a few months old and I was the only earner and pay all the bills, mortgage, gave her a disposable income etc, everything a man should do for his family. We have another child who is under a year old but our relationship has collapsed beyond rescue.

I do not want the children to lose their home so she has made enquires with the mortgage lender and CSA and apparently the following applies. The bank has said if they are given 1 years proof of CSA payments then they will be happy for me to be removed from the mortgage and the house is hers. Alternatively if she gets a court order stating I am paying the CSA at the given rate then it can be done straight away. She does not work and probably wont until the youngest goes to school in just under 3 years. The lender is happy that the CSA & benefits are sufficient to cover the mortgage.

This is not an easy spilt and she is very bitter. She is going to see her solicitor next week to get this sorted and I was going to move out into a rented house. I am now reluctant to move as she has said she will see what her solicitor advises and I get the feeling that something unpleasant is going on. Solicitors act on instruction but I think she is now out for all she can get.

I have a 17 year old from a previous relationship and pay CSA for him.

I would move out as it’s a horrible atmosphere but if I am forced to pay CSA the mortgage and rent it will be impossible. Can I be made to do this?

I cant afford to buy her out.

If we sell there will be a shortfall of £20,000 - £30,000, am I liable for the entire cost? Are we both liable? Am I liable to her or the bank? Does she get her £60,000, the bank get the rest and then I or both of us are liable to them for the shortfall?

I have a works pension, can she make a claim on this?

What would you do?