He has no interest in Harry, he winds her up because he knows she has a short temper, then sits there and takes it and says things like "Imp in the wring sorry" to look like the victim. It makes Harry look really bad, and makes him look like a little nation's sweetheart.
I feel Harry genuliy does care about him, so when he's all over Nikki, saying he would marry jade, bitching about her and winding her up (only wen other HMs are there so it looks like he has a backbone) of course she's going to get jealous and angry, but because people can't see through Nick's game playing, she's the bad one??