I've always loved Anya, and never could understand why she kept getting cast as such a bitch in fanfic.

That said, I think you're being a little hard on Xander. I think Xander made the exact right decision.
Though, in typical Xander-fashion, Xander didn't tell Anya about what was bothering him *soon* enough.

Anya,on the other hand, was forcing things, going to far, too fast, more or less rail-roading Xander, which really wasn't fair to either of them.