He's pumping Harry. Or at least trying to.
That rumour is very prevalent online. They may indeed just be mates, but they seem insuperable. I find it very odd that he never invites the other members of the band to his celeb "gatherings". Maybe he doesn't like them, or they don't like him? I can't say I blame them if that's the case. But I do remember an interview Grimmy did where he said he and Harry got on so well because they both had the same daft sense of humour, however whenever I see 1D interviewed Harry is practically mute. I see very little of a personality, let alone a sense of humour, The others seem more outgoing.