Xander was Spike's consort and they found out that Willow did some Chaos Magick so that Xander, Tara and Dawn could be the "Normal Ones"... then they had this huge argument and Xander said he never wanted to be 'normal'... I think Tara broke up with Willow when she found out about the spell...
well... that's it, if anyone can help...
EDIT: found it... its White Knight, Black Knight by Amejisuto thank you
meaura_at_home and silkensky 