"Five years ago, I went through a bi phase and used to sleep around with pretty much everyone that came along, including other men," the letter reads. "This changed when I fell in love with my new partner, who is everything to me."
The unidentified man even had plans to propose to his girlfriend, but it all fell apart when he finally met her parents.
"Halfway through lunch [I] realized that I had slept with her father," the letter continues.
As if that wasn't complicated enough, the father gave him an ultimatum.
"When my partner and her mother were away, he told me to end it with his daughter," he wrote in the letter. "Im obviously in love shall I just ignore him, or tell my partner?"
"Walk away now, and avoid the massive pain that would otherwise be inflicted on your partner, her family, and yourself," she wrote in The Guardian.
Although INSIDER can't independently verify the story, we spoke with three relationship experts about bisexuality and this unusual situation. All three agreed that the man should be open and communicative with his partner before walking away.
"Intimacy in a relationship is about knowing each other, deeply," she told INSIDER. "This isnt just about sex. Its about everything. So, until, and unless, couples are willing to be brutally honest with each other about their pasts, presents, and futures, there is no chance for deep intimacy in a relationship."
Additionally, author and relationship expert Susan Winter said they must have an open conversation because there is a chance that the relationship may survive. She said there should be some idea of openness with his female partner, otherwise, they would not be attracted to each other.
"As our society evolves, we are having greater freedom to understand who we really are, independent of stereotypical roles," Winter said. "We have to have a very honest conversation about our future because marriage is not going to look like what our parents had."
Kolawole said leaving the relationship before communicating can actually deter this open-minded future and create a dangerous cycle of sexual suppression.
"Ending the relationship because of this also maintains [or] perpetuates biphobia," she told INSIDER, "which is what I believe maintains our societys culture of leaving bi men with the only option of lying to their partners to feel safe and limiting their ability to show up in the world as their full selves."