I think that I buy it, in retrospect, because of Chosen. Because of the way that Buffy lights up when she sees Angel and the way his whole world is her again, just for when he's with her. That their love is still that strong after four years of barely seeing each other speaks volumes. Buffy was the first person that Angel loved, she made him perfectly happy. He was her first love. They'll never forget each other, never stop loving each other.

None of which means that I think they should get back together. Like they said many times -- none of the things that made their relationship impossible have changed.