I'm not sure why it's such a huge theme in fannish media properties, except perhaps that we perceive a ship as a relation of absolute trust between two people which is always at risk of disruption by betrayal

Good point (I was tempted to go off on a tangent and talk about adversaries sometimes having some sort of chemistry between them and how that would fit in with you're theory. And then I realised I would be going into the realms of fandom rather than canon *facepalm*)

Sorry it took so long to reply. RL kicked my ass this week.