Disclaimer I do not own Buffy and make no money from this story.
Knowing
Spike knew that his relationship with Buffy was weird, abnormal, and just plain strange. He also knew that he didn't give a crap what everyone else thought. There was one thing he knew perfectly clear he loved her, even if she just used him, she came to him day or night just to feel something. He really did not care what she was coming to him for whether it is comfort, pain, or sex.
It was something he could give her no one else could .she had started coming to his crypt a few nights after her friends pulled her out of what they thought was hell ,but turned out to be heaven and she was happy . How could they not know that was where she would be after all the good she's done. Only he could see how much pain she was in, none of her other friends even knew because she had to put on a happy face for them and be all normal.
The only time she was actually able to put her guard down was around spike, which was when he saw what was under all of her armor. This was just a few of the things spike knew about the Buffy he saw almost ever day.