Bella DePaulo Ph.D. has been writing about this for at least 14 years now [0]. This article is actually a good summary of her thesis and perspective which is simply society is biased against single people. Her book titles include Singleism, Alone, Singled Out, and Single with Attitude.

[0] https://www.amazon.com/s?i=stripbooks&rh=p_27%3ABella+DePaul...