(noun) A back-burner bro, or BBB, is a relationship status whereas a woman is unsatisfied with her current man sexually, so she keeps another man "on the back burner" to keep herself satisfied, whilst maintaining an emotional relationship with the first. "Back burner bros" are by high correlation significantly better at having sex than their counterparts.
Girl 1:"How's the sex with Tony??!"
Girl 2:"It's really not as great as I was hoping it would be, but we still have a lot of fun together..."
Girl 1:"Sister, I know exactly what your going through, just get a back burner bro to keep on the side and you'll be much happier!