Edited: I feel strongly about drugs, after seeing people I know go downhill so am bang against the notion. BUT I'm gonna give them the benefit of the doubt on this until someone ever gets busted on a rumour that proves concrete, which this isn't.
A lot of it seems to be based on people just not liking the Grimm. That's not good enough for me. I still like them together and there's a strong chance it's all pure gossip-mongering, misinterpretation or not as bad as it seems.
Basically they can still get married. Ignore Jaime Winstone.
I think also that even if (and I don't actually believe it) Nick were some drug dealer to the stars, it's clear he and Harry are genuinely friends as well. You don't need to hang out with your dealer that much, go for ice cream and meals out, to the cinema, to his house on Christmas Day, hang out with his mother at London Fashion Week, come to his radio show most nights. Whatever else might be going on, I think it's safe to say it's not all their friendship is based on.