It was very angsty, and it went on about how Xander had been hurt by people, all the while listening to "I love you.". I don't think it was very long, more like an one-shot.
There was this one scene, after the Faith thing, and he told her 'I love you.' to make her understand how he felt. She told him he was fucked up.
There was another scene about him doing something to Willow's barbie because she told him she loved him. One wasn't supposed to love the people you cared about.
Finally, he's with Spike. Spike looks at his scars, and is wondering about them or something. He realized that all of those had been done to the music of 'I love you'.
It ended with something like 'I hate you. Hate you so much it hurts.'.
I remember it being really, really good, but I'm looking through the Spanderfiles and I can't seem to find it. If someone could tell me what fic this one is, I'll be very thankful.
Edit: Found!! It's "I love you means.." by Becka.