Here is a quick summary I wrote for a Facebook message and thought I'd share it.
In my trilogy, a "real" couple discover a portal to another world (yeah, typical) and learn to live there, but when "he" fears being trapped there and wants to return, "she" decides to stay. Over the years she needs his help and he must return again and again. She also rescues him sometimes as they hop around the time zones, affecting history in good and bad ways.
The side story is the possibility that this sci-fi world does not exist except in his mind--that he is going insane; when he takes others to this new world and they also refuse to return (life is better there than at their dull jobs on Earth), police believe he murdered them and hid their bodies. Over the course of the trilogy he is always escaping from the police or a mental hospital to return to the parallel world...where he has become a cavalry captain, then a king, later a wiseman.