Lyric discussion by pepsipwnage1 

Cover art for Something I Can Never Have lyrics by Nine Inch Nails

its quite obvious to me that this is about a guy who's obsessed with another girl and cant seem to stop thinking about her. "i'm starting to scare myself" probably means that the guy is alarmed at his behavior. pretty much every line alludes to his obsession in one way or another, but that's just my take on it.