the fact of the matter is that buffy ends up isolated no matter what the scoobies do because she bears the burden of the slayer alone at the end of the day and nothing can change that. the problem with this isn't that she's separate from them, it's that they don't want to acknowledge that she is, and in doing so they drive a wedge between them that just grows and grows. the best thing about spike is that he's similar enough to this other side of buffy to understand it and her by extension. he is the only person around who can support that side of her.
most of buffy's issues in season six stem from the scoobies rejecting a part of buffy that spike accepts. and this shame she feels for her reliance on spike and the presence of this darkness and isolation she cannot avoid is largely because of them. i'm sick of this bizarre assumption that pointing out where the scoobies go wrong in their relationship with buffy somehow equals an uncritical uplifting of spike. just because he understands her and represents a certain aspect of her doesn't mean he doesn't fuck up. i mean that's kind of the whole point of their season six dynamic. one of his biggest issues is that he thinks he's helping her by enabling her completely because he doesn't have the ability to properly identify the line between self acceptance and self destruction - pursuit of the id is one of his biggest character traits. that's what makes the end of season six and his decision to get the soul so interesting (although of course there's just as much i can say about the narrative framing of that in regards to lore consistency and the story's obsession with angel, but that's a whole other thing).
point is, the scoobies cannot understand all of buffy, and when they refuse to acknowledge this they destroy their chances of building any bridges to even a simple relationship with that other side of buffy or helping her carry that burden in any way. meanwhile, spike is in the proper position to understand buffy as the slayer and hold his own with her in such a way, but his definition of love is wholly obsessive and destructive. while i disagree that he's incapable of love and even of loving selflessly without his soul, i think spike's version of love in particular is self destructive in a way that enables buffy's own desire to hurt herself through hurting him (see the aforementioned shame regarding her shadow self). spike cannot identify why allowing buffy to give in to her dark side in such a way is bad because he struggles to understand how she could use this to resent herself - although i do think he realizes it's happening on some level.
spike is also buffy's only form of catharsis and the only one that actually listens to what she is saying during a time when everybody else is dismissing her because of the aforementioned inability to understand her as the slayer. it's a clusterfuck - and a clusterfuck that needed to be shattered with a hammer for any kind of relief. and quite frankly to disregard the scoobies' own part in this situation does a disservice to buffy as a character. to be honest, she deserves fucking better than what everyone in her life gives her, especially the scoobies, who grow to take her for granted and feel entitled to controlling her life as a way of keeping her conformed - again, due to the aforementioned lack of desire to acknowledge this other part of her that they cannot connect with.
which leads to season seven, where spike is the only person on the show who has developed and changed enough to remain at buffy's side helping her carry the burden. while everyone else suffered during season six, none of them opened their eyes to what they were doing to buffy - and if they did, none of them acted on it. spike is the only one to acknowledge the damage he's done and work to become better for buffy in any way he can. he is the only one that ends up able to carry that burden with her because he is the only one capable of facing the truth and acting on his desire to do better.
the fucking problem isn't that he hurt buffy - because to be quite frank everybody did - it's that he's the only person on the whole damn show to acknowledge his place in buffy's life, and to acknowledge the burdens she bears, and actively change himself for her. did you know he has almost all of the genuine apologies in the entire show? seven seasons and all of the harm the scoobies cause buffy, and it's fucking spike that is acting like a mature person capable of being a proper partner.