I don't think it'd be a barrier once B/A were well and truly not an item, but I think it adds another twist of the knife and that has a strange appeal to me.

I don't think Giles is a father figure to Buffy, but I do think he could plausibly have had a primitive, visceral reaction to knowing Angel had her first. And of course, it's that exact taunt that Angelus uses with Xander when they go head to head at the hospital, isn't it?

(Oh, don't know if it's me, but the fic link doesn't work?)