So sorry OP
. You must be feeling totally shocked and sideswiped by this.
I agree with PPs on trying to get out of the mortgage. One other thing to add, IF by some miracle he is able to finance the mortgage on his own (says he'll get someone in to rent etc), DO NOT go with that. If you leave but remain on the mortgage it will impact your ability to get a mortgage elsewhere should you want to. In the bank's eyes you already have a financial commitment to the current mortgage. Don't forget that on a joint mortgage, you are jointly and severally liable for the repayments. So if he vanishes or stops paying, they will come after you for the whole amount regardless of whether you're living there or not. Any payment defaults will impact your credit record.
From what you have written about this out of the blue change in him and his attitude towards you, I would not trust anything he promises and would cut all ties esp financial ones, fully and properly so there is no link between you and him and you are free of any liability. Ultimately if arrears accumulate, the bank will repossess, sell the house as quickly as possible and come after whichever one of you is the most solvent for any deficit. Hopefully that won't be necessary and he'll just see his deposit wiped out instead
.
Ie house price £250,000
Mortgage £200,000
Deposit £50,000
Repossession sale price £210,000
Minus fees etc your EX would be lucky to see £10k deposit back.
You could also go to the mortgage company, explain your predicament and see what they can tell you. You are in a vulnerable position, to try and stay living in a house where your partner is adamant that he wants you out. Hopefully they will have some useful advice/guidance for you.
Keep a meticulous record of all convos /messages between you and him so that if you do find yourself resorting to court to press for the sale you have evidence to counter anything relevant which he may later deny.