From Revenue Website
What is the position where the purchase monies are not provided entirely by the first time buyer?
To qualify for the relief the entirety of the purchase monies, including any borrowings, must be provided by the first time buyer. Any person, who provides part of the purchase monies or who is a party to any borrowings relating to such purchase, is also regarded as a buyer of the house and the relief will not be available unless that other person is also a first time buyer.
The basis for this treatment is that, in such circumstances, the house is held for the person providing the monies used in the purchase of the house by way of a resulting trust presumed in favour of that person. This treatment applies whether or not all the parties providing the purchase monies, or all the parties to any borrowings, are actually named in the deed of transfer.
On the basis of this, you lost your ftb stamp duty status when you were a party to the borrowings.
You could argue the toss with Revenue I suppose. You should ask your own solicitor to make the application to release you from the Mortgage Deed but your partner will have to apply for the mortgage amount in his sole name.
mf