On his father's deathbed, Simon vowed that the Hastings line would die with him as the ultimate act of revenge. The Subplots Bridgerton - S01E02 - Shock and Delight [Transcript]

By pretending to be "glued to each other's side," Simon avoids mothers looking to marry off their daughters, while Daphne becomes a "prize" coveted by other men who suddenly see her as more desirable because a Duke wants her.

in any room I entered. Come. You can speak. I understood you well enough. And I will help you to overcome this stammer of yours. . Scraps from the loft Bridgerton S01E02 Recap - TV Tropes

Simon's mother died during childbirth after finally delivering a male heir. His father, Lord Hastings, was only concerned with the boy's ability to carry on the family name and showed no grief for his wife.

The episode reveals why Simon is so determined to never marry or have children through a series of flashbacks:

When young Simon developed a stutter, his father rejected him as a "failure" and sent him away to be hidden from society.

In Bridgerton Season 1, Episode 2, titled "," the narrative centers on the origins of Simon Basset’s trauma and the escalation of a high-stakes social ruse. The Main Plot: A Strategic Charade

Anthony Bridgerton is furious about the arrangement, distrusting Simon’s rakish reputation and fearing for his sister's honor. The Origin Story: Simon’s Past