Redshirt boyfriend

The fella that your girlfriend keeps around in waiting as a back-up to you. Similar to a Sancho, however a redshirt boyfriend may or may not have had relations with your girlfriend while you were dating.

Many times a soon-to-be Ex-boyfriend has met his replacement before realizing his doomed fate.

etymology: a Redshirt Freshman is an american college football term for an athlete who practices with the team, but sees little game time in order save a year of his eligibility to play for his team at a later date.