Nicole Murphy -- Someone's Cheating On Me ... And It Might Be Johnny Gill

Nicole Murphy's playing the victim in a cheating scandal -- but this one has a twist, and does NOT involve Michael Strahan ... instead it's singer Johnny Gill.

Of course, Nicole famously accused Michael of cheating when they broke up -- which he denies -- but her pal Johnny Gill decided to play up that story line for his new "Behind Closed Doors" music video.

TMZ obtained this preview ... where there's a love triangle between Johnny, Nicole, and another hottie. You gotta see what happens.