Male character goes on adult dating web site after leaving a LTR. He only wants to date and have fun now that it didn't work out with the woman he was to marry.
One particular profile catches his eye, and not only because the woman is located near him.
She seeks a casual, ongoing relationship in which she can fully explore the submissive side of herself. She's married and not looking to change her situation, but she hasn't been physical in a long time and has never tried anything like this. He immediately thinks of all the ways he can train her.
The two of them trade pms for a while before meeting. When they meet, they realize they actually know each other.
She's mortified. He's surprised but remains interested.
How they know each other is to be decided, but the more taboo or forbidden the better.