"While there are benefits to sleeping together, one partner's troublesome sleeping or annoying bed habits can affect the other and increase production of the stress hormone cortisol, thus causing issues that impact the couple as a whole," Mary Jo Rapini, a relationship and intimacy psychotherapist based in Houston, told the New York Times.
A 2016 study from Paracelsus Private Medical University in Nuremberg, Germany, showed that sleep issues and relationship problems tend to occur simultaneously. One person's lack of sleep because of the other's nighttime tendencies — snoring, restlessness, room temperature — can result in relationship conflicts.
And a 2017 study published in the journal Science Direct found that couples who didn't get enough sleep were more likely to argue.
“It’s usually the wife or girlfriend who favors the idea of separate beds,” Rapini told the Times. “Women are more sensitive to their bed mate’s bad habits, and pregnancy and hormonal changes or problems can cause them to want to sleep alone.”
Couples should examine why one wants a sleep divorce before moving to separate beds, relationship expert Margo Regan told Heathline.
"I think it's important to look at your motivations for doing it," she said. "Is it to 'get away' or 'withdraw' from your partner? Is it a way of trying to claim more 'me time' in the relationship? If so, perhaps there are other ways this can be done."