I had a friend who worked evening shift as a manager at a customer service call centre for a credit card company, his office was very near my apartment (a flat above a store) and my apartment was in the middle of his route home to his lovely girlfriend. During the day we would text and e-mail each other random stuff to make each other laugh and pass the time. He knew I worked in an office 9-5 so he'd send me NSFW stuff as a joke to try to get me in trouble. But some of what he sent me would get me hot. When I told him that, he started sending me only that. Not porn clips (videos in email were auto blocked and flagged) but pics or sections of text from a letter to Playboy, or his past experiences, that sort of thing. And I would send him that sort of stuff when he was at work and I was home. Every night he'd joke and thank me for "keeping him awake at work" and he would go home to his girlfriend.
I started sending him bits of erotic stories I was working on, just to get his opinion and once he asked for a description of himself as a character. That started texts and emails of me describing stories where he and I were involved. Very hot stories that soon devolved into just short descriptions of what we'd do to each other if we were ever alone together.