Sheldon will have a hard time adjusting to the idea of Leonard leaving him to move in with his wife, while Howard and Raj will live out the dreams of being in a band in Monday's episode of "The Big Bang Theory."

During the last episode, the guys went on a road trip to give Leonard the bachelor party that he never had. However, their plan backfired when they caught a flat tire. Meanwhile, Penny finally told her father that she and Leonard have eloped.

The sneak peek for the next episode, "The 2003 Approximation," reveals Sheldon freaking (watch trailer below).

"Now that Leonard and I are married, it kinda makes sense that we actually live together," Penny tells Sheldon in the teaser video.

In response, Sheldon gets upset and throws a hissy fit.

In the meantime, Stewart tells Howard and Raj that he is looking for free musicians to play live music at the Comic Book Store in order to attract customers and help him stay in business. That gives the guys the idea to form a unique band that combines folk music mixed with sci-fi.

According to CarterMatt, the synopsis for the upcoming episode reads as follows:

"Sheldon learns of an impending change in his living arrangements and decides to revert back to 2003, a simpler time before he met Leonard and Penny. Also, Howard and Raj form a band to play at the Comic Book Store."

Season 9 Episode 4, "The 2003 Approximation," will premiere on Monday, Oct. 12 on CBS.

Watch preview videos below.