What does the phrase I'm behind you but your behind me mean?

the truth behind something is the motivation for an action.

From the eponymous game, the phrase 'to be behind the 8-ball' means being in a difficult situation.This would seem to obviously stem from the fact that when playing 8-ball, the 8-ball must be...

It's a form of affection or a prelude to lovemaking. (Foreplay!)

Per Answers.com, to retreat, hang (back) or fall (behind) in movement, progress, development, etc. Synonyms: http://www.answers.com/topic/fall-back-and-forward, http://www.answers.com/topic/lose,...

It is a saying about how something is not working or is spazzing out. EX: "The copier was on the fritz."