How much negative equity do you have?
Better if you check your redemption figure with your bank in case there are additional charges like early repayment.
Are you counting the �14k deposit in the negative equity or is the mortgage and any other charges over what you would get for the house alone?
Have you accrued any mortgage arrears as yet?
To get his deposit, unless you sold, he'd have to go to court to get an order for sale although the negative equity situation isn't great from the lender's point of view.
Could you speak to your lender about trying to manage the payments better or taking a payment holiday?
If there is an ex trying to get an order for sale which would not pay back what they owe then they may be more helpful to get the equity up.