This is from the Revenues own website - and it clearly has in mind that you either purchased or built ...and wickedly.. if your partner did and is on title ..then you are not a FTB.
"...A First Time Buyer as defined by Section 92B, Stamp Duties Consolidation Act, 1999, is a person, (or, where there is more than one buyer, each of such persons):
who has not on any previous occasion, either individually or jointly, purchased or built on his/her own behalf a house (in Ireland or abroad) and
where the property purchased is occupied by the purchaser, or a person on his behalf, as his/her only or principal place of residence and
where no rent, other than rent under the rent-a-room-scheme, is derived from the property for five years after the date of the current purchase ..."
Does that help?