Sheldon Cooper and Leonard Hofstadter were far closer than roommates and friends, they were brothers. Throughout these two have pushed each other to the limit and tested each other's patience. Sheldon didn't think Leonard made the same sacrifices he did, and Leonard thought Sheldon was impossible to live with. And yet, the two couldn't live without each other.
Leonard wanted more than anything to get out of Sheldon's roommate agreement and start a life with Penny but there was a small part of him that would miss Sheldon. They had subtle moments as best friends that should be appreciated and remembered by fans.
Professor Proton was a hero of Sheldon's growing up. . But when Professor Proton passed away, Sheldon was stuck in a state of shock. He and Professor Proton weren't close by any means but Sheldon looked up to him immensely.
That day, Sheldon took a nap where Professor Proton visited him in his dreams. When he woke up, Leonard was there to check on him and make sure he was okay. In a sweet moment, Sheldon hugged Leonard without saying a word. It was one of those moments that left Leonard (and fans) speechless.
In "The Status Quo Combustion," Sheldon has a hard time dealing with the constant changes in his life and has a minor meltdown. The only thing that could possibly bring him happiness was hopping on a cross-country train ride.
Sheldon eventually made his way back to California but got stuck in Arizona when someone robbed him and took his clothes. Sheldon was detained at a police station in Arizona and needed a lift home. The only person Sheldon could think to call was his best buddy Leonard (much to Amy's chagrin).
Sheldon and Leonard were on their way to a conference when they realized they weren't that far from Skywalker Ranch. With time to kill, they pulled over to see if they were able to go on the property. The security guard was nice enough and told them they weren't allowed on the property but he would grab them a t-shirt or two for the ride home. Sheldon was too close to happiness, though. . Sheldon and Leonard were then thrown into a holding cell until they were cleared to leave. Instead of viewing it as one of the worst experiences of their lives, they both decided that it was a magical adventure because of what they saw and how close they were.
When Raj's sister Priya comes to town, Sheldon finds out that Leonard slept with her. He was mainly hurt because Leonard broke the roommate agreement but he also felt bad for Raj. and created a lie for him to tell his friends. Leonard wasn't really able to sell the lie, but Sheldon had his back either way.
When Sheldon and Penny became engaged, Sheldon knew that his one-on-one time with Leonard was dwindling. To make things easier for Sheldon, Leonard and Penny agreed to keep their living arrangements the way they were. (They did live across the hall from each other, after all.) and things came to a head. The two friends went back and forth with each other and vented about their irritations. They eventually realized they were upset with each other because they loved each other and were nervous about what the future would hold. They agreed to put their daggers down and be nicer to each other.
It was a big moment on when Sheldon finally took the plunge and married Amy. They could have gotten married at city hall but Sheldon wanted their union to be special. They had a big wedding with all of their family and friends in attendance, and Leonard was chosen as the best man. The two friends shared a special moment before the big day where Leonard told Sheldon that he was no longer his problem anymore — . Sheldon jokingly said he'd always be Leonard's problem and they hugged gleefully.
In "The Bon Voyage Reaction," Leonard had the opportunity to work on a project at sea with Stephen Hawking. Penny and Sheldon were both sad about Leonard leaving them but promised they would take care of each other. They threw him a going-away party where Sheldon told the room that Leonard was his best friend and he wished him well. With Leonard gone, and learned to trust each other. which also strengthened their bond with Leonard.
Sheldon doesn't do well with change. He's a man who loves consistency and what he's getting himself into. When unexpected roadblocks stand in his way, he panics. In "The Status Quo Combustion," change continued to find Sheldon, and he panicked after finding out the comic book store burned down. He ran away to the train station where he could find solace. Leonard became worried when Sheldon didn't come home and did everything he could to track him down. Because of their friendship, while tears came to his eyes.
Was there anything more endearing than when Leonard got nose surgery and Sheldon did everything in his power to stop him? Leonard told Sheldon and Penny he had trouble breathing for years and was finally able to do something about it. Sheldon was against the surgery because he found Leonard's snoring comforting. He was also scared of losing Leonard if the surgery went wrong. Watching these two do everything to save each other's feelings was what best friends were all about.
In the third season, Leonard's mom, Beverly, is in town visiting Leonard. Sadly for him, the trip goes sour. It became clearer than ever that he and mom would never have a close relationship. She told more information about their family's ups and downs than to Leonard! After hearing that his parents were divorcing and that his family dog died, Leonard went to his room to sulk. Sheldon knocked on the door and adorably tried to make him feel better. It didn't work the way he expected but it proved that Sheldon truly cared for his friend. "Just remember, Leonard. Where your biological family has failed you, you always have me," Sheldon said.