The rumor floating around is that Niall is dating model Olympia Valance. It's just a rumor at this point however. Olympia did an interview not to long ago and didn't confirm that the two were dating.
She told the Scottish Sun “We’ve known each other for a couple of years now. He obviously spends a lot of time in Australia with his cousins. We just met in Australia and we’ve been messaging ever since and yeah we have hung out together a bit,” and she added "We are quite close. I see him when I come to London and he sees me when he’s in Oz."
So you can see where the rumor is coming from but even though they've "hung out" together Olympia claims that she is SINGLE at the moment. Who knows what's going on???