Sebastian was Sheldon Cooper's former roommate before Leonard Hofstadter. He was only seen during a flashback in the episode "The Staircase Implementation" (S03E22) when Leonard tells Penny the story of how he first met Sheldon back in 2003. Sebastian's name is only given in the credits of the episode.
A Roommate Agreement is a written contract between roommates that outlines their rights and obligations while living together. This agreement includes house rules, maintenance duties, restricted behaviors, and more. For a Roommate Agreement to be useful, everyone sharing the household must agree to it.
It seems when Sheldon was accepted at Caltech, he was afraid to move away from home and Tam offered to move out with him and then he didn't do it. Tam found a girlfriend and stayed in Texas. Amy explained that if Tam had moved out there with him, he wouldn't have the great friends he has now.
However, it's crucial to remember that while your roommate agreement is a binding contract between the roommates, it's not the same as a formal lease agreement. Thus, any eviction based on it must still adhere to Florida's landlord-tenant laws.
We know that Missy became a waitress at older age, got married, and had 2 kids with her first husband, and had 2 kids with someone else. We don't know who her first husband was, but it is implied to be Billy Sparks. Some fans speculated that Missy got remarried to Raj Koothropalli and they had 2 more kids together.
Leonard tells Penny about how he and Sheldon became roommates and what happened to the elevator. Leonard tells Penny about how he and Sheldon became roommates and what happened to the elevator.
The Staircase Implementation - The Big Theory (Season 3, Episode 22) - Apple TV.
A flashback in the season three episode “The Staircase Implementation” reveals that the two characters met when Leonard applied to be Sheldon's roommate. That moment, we are told, was “seven years ago”, and the episode aired in 2010, meaning that Sheldon and Leonard presumably met in 2003.
A flashback in the season three episode “The Staircase Implementation” reveals that the two characters met when Leonard applied to be Sheldon's roommate. That moment, we are told, was “seven years ago”, and the episode aired in 2010, meaning that Sheldon and Leonard presumably met in 2003.