As an Irish person, I can advise that people here can be homeophobic; like others elsewhere. Irish B&Bs are usually owned and run by very religious, middle-aged/elderly women; but in my experience, they don't seem to care if a couple is unmarried and sharing a room. My advice would be to just not mention the fact of your being gay at all - is it anyone else's business? I do think that might be best. The old girls might be embarassed if you try to discuss, but if you wish, you could ask if they minded. Personally, I wouldn't.
Incidentally, try visiting the tourist board-approved site www.townandcountry.ie. They can send you a B&B book. Do come up and see the Giant's Causeway, it's amazing! And the Bushmills Inn Hotel does very good food, as does Killens (both also do accomodation. Pricey, but really good cuisine is very hard to find in N.Ireland, believe me. Both have websites.)
I do hope you come over.
Ashaw McKenna