Thank you for your question
My name is Clare
I shall do my best to help you but I need some further information first
Did you protect your investment with a Declaration of Trust?
Sorry - if you mean the telephone pop up yes it does - and you should ignore it
Do you have any evidence of the £9,000 deposit
How much is the house worth and how much is outstanding on the mortgage?
is he likely to agree to sign something to protect you now
Given that you paid the deposit and that it is clear that he has always accepted that the property was "joint" you have a clear financial claim on the proceeds of sale and could enforce that using the Trusts of Land and Appointment of Trustees Act.
In order to protect that you could potentially register a restriction at the Land Registry OR you could ask your ex to simply sign a straightforward written agreement confirming that he will pay you half of the proceeds of sale.
It does not need to be a complex document - a simple straightforward letter would do - and if he then did not pay you you could use that as evidence of the agreement.
I hope that this is of assistance - please ask if you need further details
You are most welcome - I hope all goes well