"Life goes easy on me" means that life hasn't thrown him any bad things like a bad breakup or a harsh death in the family. it's only used in this song, you wouldn't use it in normal conversation.
"The pupil in denial" I think is referring to the pupil in the eye. It either can't believe she's dead or can't believe she's so beautiful. I've never heard the song, I only looked up the lyrics so I may be wrong there.