Wholy different from fics where Buffy and Angel are constantly nattering on(to quote Giles) about being each other's mates.

Oh, but I can totally see that. When Buffy is on 'Beer Bad' beer.

I kinda feel like Buffy would sock him in the mouth if Angel called her his mate. What I don't mind, though, is when the word is used to describe a base animal drive that his vampirism enhances and works with or at odds with a human romantic impulse. I can see Angel thinking of Buffy as his "mate" in that sense. And being ashamed of it.