Dream come true sort of

John's roommate, Corey, had started dating Felicia, a blonde hottie, and John was jealous. The two were in the honeymoon phase of dating, where she would come over every day and they'd disappear into Corey's room for long hours.
John had been single for a while and one afternoon, after Felicia had come over and slipped, giggling, into Corey's room, John wished he had the relationship they did. As if in answer to his wish, the world changed.
Suddenly, he was lying on his back in bed staring up at his roommate. One of John's hands was wrapped around Corey's warm shaft, the other was cupping a heavy breast. Before John could even speak Corey's cock pulsed in his hand, sending a spurt of hot cum across John's tits. 
John gasped as the warm seed slid down his skin. He gaped down at his body and saw Felicia's wonderful figure, her legs spread to reveal her wild bush, the pussy lips still glistening, his body still warm from Corey's fellatio.
There was a man's scream from downstairs, and seconds later the door to the bedroom burst open. John's old body stood there, staring in horror at the sight. Corey looked up at her, then down at his dick.
"Whoa, I've got a penis," Corey said.
They'd all been victims of the Great Shift. Corey had swapped with the teenage girl in the apartment downstairs, while John and Felicia had swapped with each other.
In comforting each other, John and Felicia grew closer and closer, until one day they hooked up to explore their new bodies together. John's wish had come true, though not exactly in the way he'd expected.

A college student discovers the ability to hop into people’s bodies, and uses his new power to take over his cute crush and explore her life in How I Became a Hopper, on Smashwords or Amazon. Preview here.