There is No Ethan by Anna Akbari

The author met "Ethan Schuman" over a dating website and fell hard for him. But every time she tried to meet up with him in person, he cancelled. That began to annoy her and make her suspicious about Ethan. She tracked down another woman he had dated, Gina, who had the same experience. Together, they tracked down a third woman, British Anna, who had fallen for Ethan's charms for much longer--two and a half years, which really messed up her head and her life. She too had never met  Ethan in person. The three women joined forces to track down Ethan and were shocked to find Ethan's real identity. Even after they confronted Ethan with the truth, he kept contacting them to maintain his hold over them--and tried to get them to turn against each other.  As their story got out, more women who were victims of Ethan's mind games appeared. The three original victims tried to let the people in charge at Ethan's university and later at his job know what he had been up to because they really thought he needed therapy, but their efforts weren't very successful.

Though this is a little too much detail about the back and forth between Ethan and the author, this is a compelling story. I have to say, I do wonder why these intelligent, successful women put up with Ethan as long as they did (before discovering his real identity). In his communications with them, he was often rude, abrupt, and dismissive. And he kept having them make plane and hotel reservations (at their expense) for the get-together trips that never happened. But apparently the good parts of their conversations with Ethan were enough for them to hang in there in hopes of having a future together.