This song describes two people who used to really love each other, but now the feelings aren't as strong and things are getting worse for them, which is starting to cause some confusion. Some lyric analysis:
"My heart's on an auction, it goes out to the highest bid" - He is staying in the relationship for now because of what they had, but if he finds someone better, he might just take the offer.
"But there's an option, to die is to live in her head" - He is almost willing to kill himself just so the girl can remember them for who they were and what great things they had before it is too late and the good memories will be replaced by the bad.
"So I'll hang on, never let go, I dug this pain into my chest" - This can translate to the guy suddenly feeling confident and tenacious about making their relationship work so they can be happy again. It's also saying that he kept the pain and sorrow to himself and is ready to just make things work. >>