Hm...I'm not much for bashing Xander, but there's a wonderful fic that has him accept and come to terms with both his feelings for Buffy and her feelings for Spike- and it's quite a bit of torture for poor Xander, too, which I'm guessing you'd like

-
Strangers by Sosa Lola.
I'd also recommend almost anything by Dreamweaver if you're specifically looking for that kind of anti-Xander fic.
(And not to self-advert or anything

, but I did write a ficlet in which Xander comes to terms with what he did in OMWF- it's not Spuffy, though, so I won't post it here, but you can PM me if you're interested in reading it.)