It's not like Spike was an enemy. Enemies meant something, they were important enough to matter when you fought. Spike was… he was a diversion, something to waste his time with when they were both still evil, and a distraction after the soul.
Not quite an enemy, because he took out his enemies, except when he didn't.. Just annoying, dangerous, but not an enemy. Just a petulant child really, testing out his boundaries, trying to get daddy to pay attention. Hell that's all Spike had ever done.
So why, knowing better than that, couldn't he help giving in to it?
It hurt, the distrust, treating him like the enemy, the bad guy that they all had to fear. Not like he wanted them to like him, except when he did. Not like Angel mattered, only… he did matter. And it hurt.
It hurt trying to talk to Angel and once again being the enemy. Sure he didn't like Angel either, but they were family. And he couldn’t do nothing while the big lug was throwing himself headfirst into hell.
Not that he cared, but hey, white hat now, had to protect the stupid from making a mess of themselves right?