The longer his obsession with Kurt goes on, the less it makes any sort of sense.
Him being angry at Aaron? Okay. Even though Nick's clearly taken that to a psychotic extreme, it's not difficult to see why those two have beef.
But Kurt? Kurt barely did anything to him. He even stuck it out far longer than anybody else in Lawtube.
Nick is an asshole, and maybe that's all there is to it, but this is now pathetic even by his already low standards. It's been going on for over a year now, and Kurt largely just ignores it.