
Parker has a problem with overcompensating his sexuality through denial. Not only is he gay but is not even attracted to humans.
Like that rich bloke off Angel, he finds demons float his boat more so than his own species. So Parker was always so miserable, using the stud-on-campus thing as a shield against the judgements and social rejection that would no doubt go along with the revelation of the truth about him.
I mean, there are blokes out there who would, no doubt, wonder what kind of man could sleep with the Buffster only the one time and then leave it like that. Well, it all makes sense if you think about Parker's real inclinations.
Kulak was a very masculine yellow-skinned demon. He reached his untimely death during Slayerfest '98. But one might wonder why exactly he had attended Slayerfest in the first place. For the Gorch couple, for example, the motivations were relatively blatant but Kulak pretty much kept himself to himself. He couldn't hide the intense anger and frustration that he felt though. Kulak was very unfulfilled in life. He was, by nature, a relatively laid back and trouble-free demon but rejection from society lead him to turn to the dark side.
He became angry, hostile.
Unlike Parker, Kulak dared to reveal who he really was and his demon friends cast him from society. Kulak was attracted to human males, look at the harsh and angry way he treated the hunter guy, Frawley: "Do you want me to cut that leg off for you?" He was unable to cope with the world anymore and its perception & judgement of him so he entered Slayerfest '98, knowing he wouldn't survive it but not caring. If he could kill the Slayer then he would have done something that would have him accepted back into the demon community. If the Slayer killed him then she was really doing him a favour.
How was he to know that it was indeed the Slayer who would have a short-lived affair with the man who would have solved all Kulak's problems? How was Parker to know that one of the many girls he used, Buffy, had a connection only a year previously with the demon of his dreams. It's quite a tragic story. But who knows, maybe one day Parker will find happiness in his quest for real attraction.
