In it Xander would never, ever leave Cordy willingly.
My two cents about it is Xander's standout trait is his loyalty -- you can plausibly set him up with pretty much any of the girls in the early cast, but once you do, it's very out of character for him not to stick to that relationship with tenacity. I can see him not handling conflict within a relationship *optimally* simply because he doesn't have good role models *or* past experience to work from, but he's fundamentally a loyal and steady sort.
(In particular -- yes, he had a huge crush on Buffy. He's not going to cheat on anyone else *even* if Buffy's throwing herself at him, and if she tries to flirt on him to make Angel jealous *while he's dating anyone in the gang*, he's going to respond very negatively to that. He tacitly let it slide in canon because of the unrequited crush *and* because he didn't have a relationship at the time; if you change the circumstance there, he's going to be *seriously pissed*.)