Dear Sir/Madam, Bacground - I split from my partner at the

Dear Sir/Madam,
Bacground - I split from my partner at the time (we have no children together) in June 2010. The relationship had become quite toxic and without blaming any party we thought it best to split. We had a house together with a reasonable mortgage and a loan that isn't secured against the property.
We agreed to put the house on the market and sell it, while this was happening I agreed to pay half of the mortgage and half of the loan. I did ask the mortgage lender whether I could take on the mortgage on my own but due to my financial position at the time turned the application down.
It sat on the market until approximately 2012 when we received an offer 5% below the asking price. I was told by my ex partner that she would agree to the sale if I paid her £4000. I didn't have this kind of money and as far as I was concerned all debt and assets should be split 50:50. I looked into the situation and found the only way out to be a forced sale, the approximate cost would have been £2000 (which I didn't have) but also when forcing a sale the chance of acheiving a reasonable offer is low.
I agreed under duress, to let my ex partner stay in the house until her youngest daughter had left school.
My ex partner drafted an agreement with help of a friend for an agreement whereby she pays the mortgage and the loan (the majority of which paid for house refurbishment) until the house is sold.
The agreement ends next year, but there is a part which states the house has to go on the market November this year unless either part wants and can buy the other out.
I started communication in December about her plans so I can make mine. Her initial reaction was to say she wanted to buy me out by an agreed percentage. She then asked if I could buy her out to which I answered 'this depends on how much she wants'. She dropped me an email to say she is getting advice and we were to meet over a month ago via her work email. I responded to the message confirming date and time. on the day of agreed meeting I asked for the location and was told she couldn't make it she was still waiting on advice. since then I haven't had a response from emails sent on the 16/04 and 22/04. We work for the same company and I obviously don't want to cause issues and appear to hassle her but I am concerned there is more going on in the background.
Can you give me advice on the best way to handle this situation and would the agreement still stand, am guessing yes as I signed this of my own volition even if I felt I had no other choice?

Best regards
Martyn