I've often heard fans complain that Buffy didn't tell the other Scoobies about how she had treated Spike in S6, even though they knew about a lot of Spike's bad behavior towards her (the stalking in S5 and the attempted rape in "Seeing Red"). I have some not-entirely-coherent thoughts on the matter that don't quite constitute an defense, mainly because I don't disagree with this complaint. I merely think that many of the complaints are overblown. I think Buffy should have told the Scoobies, for her own benefit as much as Spike's. I don't think it was fair that the Scoobies only knew the parts of the story that made Spike look bad. That said, given how much effort she put into making it up to Spike how badly she treated him, I'm not too upset about it (She certainly was a lot better about Spike in S7 then he was in AtS S5 when he encountered the soulless vampire that he had used and abused, but I digress). But still, I have thoughts that might make up a quasi-defense.
First of all, I'm not sure that telling the Scoobies about Buffy's bad behavior would have benefited Spike very much. Sadly, I'm not entirely sure that the Scoobies would have cared how Buffy treated Spike in S6. I remember what Faith said in “Faith, Hope, and Trick”: “[I]f doing violence to vampires upsets you, I think you're in the wrong line of work!” (Buffy argues with a lot of the things Faith says, but not that one.) I really can’t imagine Xander (who almost killed Spike in “Entropy”, after fighting by his side many times, just because Spike slept with Anya) or Giles (who tried to have Spike killed after he got the soul) caring much about how Buffy treated her soulless vampire lover. At best, it might cause them to worry about Buffy, but given that the Scoobies looked the other way when Buffy displayed other symptoms of not being mentally all there in S6 (not mention the non-reaction to her attempt to kill Faith back in S3), I'm not even sure they would do that. Now, Willow might have more sympathy for Spike, but Willow also has really warped ideas about appropriate behavior in romantic relationships. I wonder if she would understand how wrong Buffy beating Spike up in an alley was.
The only one I could imagine really getting it and caring would be Dawn. I’ve always thought that Dawn would have a harder time forgiving Spike for the attempted rape than Buffy, because Dawn had a rosy-eyed view of Spike. He was Her Hero. Buffy never really had any illusions about the vampire who promised to kill her the first time they met, but Dawn looked up to Spike. I wonder if knowing that the abuse went both ways in that relationship would make a difference to her.
Another thing to keep in mind is that the only reason any of the other Scoobies knew about the attempted rape was because Xander barged in on Buffy right after it happened and figured most of it out from what he saw. Buffy lied to Willow when she came into the bathroom, and said that nothing had happened. When Xander started to bring it up in front of Dawn, later, Buffy pulled him into the other room. Dawn only found out about it because Xander told her when Buffy wasn’t around, even though it was obvious that Buffy didn’t want Dawn to know. If any of the other Scoobies know, it wasn't made explicit to the viewers.
Buffy did try to keep her friends from finding out about the attempted rape. It seems that as far as Buffy is concerned, what happens between her and Spike stays between her and Spike, whether it’s his bad behavior, or hers.
One last thing: Buffy is very bad at articulating her relationship with Spike. The words “complicated” and “confusing” come up when she tries. The one time she brought up the rape attempt directly to Spike, she said, “I don’t have the words,” which seems to apply to their relationship in general. Buffy seems to have difficulty articulating her relationship with Spike even to Spike. In “Seeing Red”, when Spike asks her why she didn’t let Xander kill him, Buffy says, “You know why.” Spike doesn’t, but Buffy thinks he understands what she can’t say.