So much rage at this scene. Because it's clear that his problem is that they were having a relationship behind his back, not simply that Buffy trusted Spike, since she (and most of the Scoobies, including Xander) has been doing that since like, the fifth season. It's the relationship, the sex (his disgust at which is seen in Entropy, in that same scene I quoted earlier), that bothers him.
And this has nothing to do with Xander having already seen what happens when Buffy mixes her calling with her personal life? If Spike's chip stops working it's Buffy who would have to deal with him. Last time her boyfriend went berserk the result was many dead people. Of course Xander would rather not see a repetition of that. And yes, he is hurt that Buffy needs to hide that from him, especially considering the previous time the gang thought Buffy was sleeping with Spike they thought it was a silly idea but tried to be somewhat supportive nevertheless. "What were you thinking is a pretty natural reaction", IMO, although he should be asking Joss that, not Buffy. 😀
Parker isn't one of her best friends though. He's someone she wanted to hurt, and justifiably so. He intentionally mislead her and treated her like trash. I don't think Buffy's fantasy about hurting/showing up Parker is comparable to Xander's fantasy about hurting Buffy.
Hurting Buffy? The who in the what now?
He's not entitled to affection or love from Buffy, but he acts as if she deserves to be hurt.
He does?
Maybe, but his tone is incredibly dismissive and even in 'Dead Man's Party' he likens her situation with Angel to 'boy troubles'. It's unfair of him to judge her in that way, IMO. I don't think any rational person could ever call what Buffy went through 'boy troubles'. Something obviously traumatic happened to her in Becoming, even if he didn't know what actually went down. I can't help but think that he wouldn't have so condescendingly dismissed Buffy's feelings if he actually respected her to make her own choices. Buffy messes up, but it's clear after Passion that she carries Ms. Calendar's death on her own shoulders. She's embraced her duty as the Slayer before, even sacrificing her own life in 'Prophecy Girl'. She really doesn't need Xander to judge her so harshly. And yeah, I get that it's harsh and it's a tense situation, but does he ever apologize? No...
Well, Buffy thinks she needs Xander. I would argue that the last thing she needs is a yes-man. Buffy isn't infallible. As for respecting her choices, he did that for months while Angel kept on killing. Everyone has a breaking point. Buffy's choices had cost many lives already, I can't really blame Xander for wanting to put the whole nightmare behind him. And Buffy's tone is just as dismissive of Xander's viewpoint in DMP and Revelations as his was of hers. Yes, two wrongs don't make it right but why is it that Xander is held to some impossibly high standard while Buffy gets the benefit of the doubt? I don't see many people claiming that Buffy doesn't respect Xander after having compared his right to talk to that of "You by the dip" in DMP and accused him of "spying on her" in Revelations. They were fighting. Stupid things were said, doesn't mean all of them were meant. When push comes to shove Xander does follow Buffy's lead to the bitter end, so he must be quite a schizophrenic if he does that and at the same time thinks he knows best and how Buffy can't make a good decision to save her life. As for not apologizing, a lot of times it's implicit and a lot of times not even that. Xander is hardly the only one who does it and considering that every time there is a Scooby quarrel he is not the only one who rants at the others either there is an awful lot of apologies we might demand if we want to be pedantic. Did Buffy apologize for the things she did in When She Was Bad? Nope.