yup narcs are bad news... But this is a law forum. No-one here can diagnose someone based on a few posts... I tend to refer to my ex simply as a nutter.
Some people are certainly less capable of negotiating reasonably than others... With those sorts of people who need to stare them down and realise that they are almost intuitively/ instinctive/ manipulative / strategic than your average punter.. In my case the ex genuinely believed she was entitled to 105% of the joint assets despite never doing a days work through the relationship - YUP 105%...
So in this person's case - She genuinely thinks the ex is 'forcing' her to pay half the mortgage.. If she stops she will get nasty messages, she will be told she is ruining both his and her credit rating... She will be told that when it goes to court she will be forced to pay the money back with interest blah blah it will be intimidation and not even a little bit illegal unless it is threatening.... But until the dynamic changes he won't mention the OS assets and will continue living in a house and only paying for half of it.
Well spoken....
One thing the OP may have forgotten to take into account is the rental value of the property. For example, my ex moved out of the family home to her mothers house, i am left here paying the mortgage on my own.
For the settlement, what i do is, I tally all my mortgage payments then weigh that against half of the rental value. You see, my ex owns half the house, but she is not benefiting by living here, so she is entitled to half the rental value!