Okay, I don't know what you guys are talking about; they have OBVIOUSLY had sex with each other!!! First of all, vampires are very sexual creatures. They never seem to have a definite sexuality: biting and drinking victims is sexual to them, and they've sure fed on members of the same gender. Secondly, Angel and Spike are in the same vampire family, and vamp fams are sexually open to each other (ie Angel/Dru/Spike). Third, vamps are into the whole sire/senority thing, and Angelus being the sadist that he is... there's not a doubt in my mind that he's made Spike *********** (fill in the blanks, lol)! Additionally, Spike really admired and looked up to Angelus... of course he wanted him. Not to mention Spike's a total masochist. 😛
And if that wasn't enough to convince you, have you seen the subtext?!!