backpocket boy 

A lover that you put in your "backpocket" for a later fling.

I didn't quit David, I just made him my "backpocket boy"

backpocket boy by KittyGirl2 November 3, 2007

Back pocket boyfriend 

The ex-boyfriend that you give false hope of getting back together with when you(the ex-girlfriend) find out he's interested in another female.

ex-boyfriend back pocket boyfriend

Back pocket boyfriend by PlanetKiKi September 26, 2015