Thank you for your question
My name is Clare
I shall do my best to help you but I need some further information first
How much is the house worth and how much is outstanding on the mortgage
What other assets and debts are there and what income do you each have?
What income do you each have?
How much is the mortgage payment?
Why are you paying it when you do not live there?
Are you also paying child maintenance?
In fact all that you are liable to pay is child maintenance at 12% of your gross income (at most)
On top of that you could have offered to pay half of the mortgage - but it is far from certain that the court would have ordered this.
In addition if your ex brings her partner in then you can ask the court to order the immediate sale of the property - and it is likely that the court will agree - and order a 50/50 share of the proceeds of sale.
I hope that this is of assistance - please ask if you need further details