If you have to bash characters to make a pairing work, you probably should just give up.
Turning Xander into an OOC asshole/rapist/moron isn't going to make your Buffy/Spike or Buffy/Angel fic work. I'm sorry to have to break that news to you.

Xander is not a major obstacle. On the show, when did he ever go out of his way to make her not date someone? He may not have *liked* it, but he didn't try to make her choose between him and Angel/Spike. So yeah, stop it. Stop it right now.

Xander thanks you for your time. He also says you kind of suck if your pairing is CANON and you have to resort to name-calling and dragging his reputation through the mud.