Messy split up and don't know what to do England

Hi and thanks for reading, ive been burying my head in the sand because the whole situation has made me ill but need to try and get everything sorted.

I was with my ex for 11 years. I left the house 18 months ago.

When we got together she had 2 kids, we then had 2 of our own.

We own a house *together" ie both our names are on the mortgage. I put the entire 30k deposit down, and I paid the entire mortgage for the whole time I lived there, and for the first 5 years I paid all bills. I also provided use of a car and paid all running costs/insurance.

I had renovated the entire house (4 bed 3 story town house) at my expense, she would never help even clean a paint brush, instead would sit on her phone and scream at me that the house isn't clean and tidy etc.

I ended up going to stay at my parents because I couldn't deal with persistent abuse from her, I was basically being used to fund her life and couldn't take it any longer.

Long story short, I'd only been gone 2 months, she moved someone else in, changed the locks, and moved someone else in, and basically stolen everything I own.

Oh and there isn't a declaration of trust because when I told her I wanted to get one when we were buying the house she convinced me that I didn't need to do that because she wasn't that sort person and would never bla bla bla...... Yes I know, lesson learned.

I've now been unable to work at all (anxiety and depression) so am unable to work and therefore stopped paying the mortgage. She eventually ended up paying it after waiting 6months (clearly trying to call my bluff).

I don't know what to do.