Win Back Meaning

(transitive, idiomatic) To get (someone) to be one's partner, after having been apart.

Example:   He lost $1000 in one hand, and spent most of the night trying to win it back.
2006 July 14, “Obama Works to Win Evangelicals Back for Democrats”[1], npr:
  Illinois Sen. Barack Obama talks with Renee Montagne about his call for Democrats to reach out to evangelical Christians. Republicans have long laid claim to that powerful voting block. He believes that Democrats can win them back with issues like the drive to end poverty.
  John, my ex-boyfriend, said he wanted to see me again, so I told him how much I wanted him in an effort to win him back.