best ex ever (B.E.E.)
What your ex calls you after he/she realizes that you are the best he/she will ever have, because you treated them so damn good when you were together. No one will ever compare.
As her new boyfriend, my job is to be the best she's every had or will ever have, so she'll one day call me her best ex ever (B.E.E.). She'll be ruined on all other guys henceforth.