Have a read of
A guide to splitting up while in negative equity to outline some of the principles involved.
Who is the lender?
What is the interest rate e.g. SVR @4.5% or tracker at ECB + 0.75%?
As your ex is occupying the house, he should be paying the market rent for the property. Let's say that is €14,000 per year.
If he pays this directly to the lender, then your position in relationship to each other does not change. On top of that, you should pay an equal amount of capital off the mortgage each month. If he can't do that, then the other should not do so either. If one of you pays more capital than the other, it would be unfair.
If you had the money, you should give him roughly €80,000 or half the shortfall and come off the deed and the mortgage. However, you don't have the money and the bank probably won't allow it.
The bank may refuse to allow you to go interest-only, but in reality, if they get at least the interest, they won't take any further action, apart from hassling you with phone calls and letters.
1) The bank will not prioritise a house for repossession if they are getting the interest paid in full.
2) The bank will not allow you take your name off the mortgage. Anyway, it would be unfair to leave your ex with all the negative equity. If you could pay him, €80,000 it would be fair.
You and he can do a separate agreement whereby you agree to waive all interest in the house and he agrees to make the repayments. But you are still liable to the bank for any shortfall.
3) They might do such a deal, especially if it's a tracker mortgage. Not sure if this is the best plan though.
The bank have requested that we stop paying the short term (credit union/credit cards/car loans) debt and focus on the mortgage.
You should clear the most expensive loans first especially the credit card and the credit union. If the bank is getting interest only, they may give out, but they will just have to accept it.