Who would have thought that Dr. Sheldon Cooper would have gone on to marry a brilliant woman he met online? Funny enough, The Big Bang Theory fans have Raj and Howard to thank for this. If there's one person in the world of sitcoms who would be totally fine growing old without a partner, TBBT fans would suggest it's Sheldon Cooper. But after meeting Dr. Amy Farrah Fowler, their unique quirks and interests took ahold of one another. From seasons three to 12, we've seen Amy and Sheldon battle their differences and follow their hearts. These two were meant to be together; it just took years of baby steps and patience to get to a level both were comfortable with. From holding hands and sharing a bed, let's take a look at the couple's biggest relationship milestones.

THEIR ICONIC VALENTINE'S DAY KISS ON THE TRAIN

Sheldon Amy first kiss on Big Bang Theory.

In "The Locomotion Manipulation," Amy finds a way to have a romantic Valentine's Day that Sheldon would actually like. Together with Howard and Bernadette, the couples join for a double date on a vintage train with dinner, drinks, and conversation.

RELATED: Big Bang Theory: 10 Scenes That Never Fail To Pull On Our Heart-Strings

But leave it to Sheldon to mess things up and care more about the train than Amy. However, as the two come head-to-head about their desires for the night, they lean in for a passionate and steamy kiss. One that's so fiery that it left both of them speechless.

THE FIRST TIME THEY SAID 'I LOVE YOU'

Sheldon and Amy posing for a picture at prom in TBBT

After the gang starts talking about their sad prom experiences back in high school, they decide to throw an adult prom for themselves on the rooftop of Sheldon, Leonard, and Penny's apartment building. Sheldon and Amy went together, of course, but tensions were high. With rumors of "getting it on" after prom swirling in the air, Sheldon got a panic attack. He wasn't ready for that step with Amy. Instead of engaging in the act of coitus, the two declared their love for each other instead.

WHEN SHELDON FLEW ACROSS THE COUNTRY TO PROPOSE

Sheldon proposes to Amy in The Big Bang Theory

Fans were furious when Dr. Ramona Nowitzki kissed Sheldon without his consent. She knew he was a taken man and very dedicated to Amy.

RELATED: 5 Subplots That Were Wrapped Up Perfectly In The Big Bang Theory (& 5 That Weren't)

That didn't stop her though. After she kissed him, he excused himself from his office and flew to New Jersey (where Amy was placed for a study) and proposed to her. After kissing another woman, he knew he never wanted to kiss anyone but Amy again. Amy (and viewers) were proud of Sheldon for taking this step in their relationship; a step they were ready for.

THEIR DREAM WEDDING

After the two became engaged, the wedding planning began! The two adorably used science to plan most of their wedding, even though it didn't always work out (like who the ultimate maid of honor/best man was) in their favor. At the end of season 11, the pair had their wedding along with showing us Sheldon's potential for a new theory with string theory. Amy looked like a beautiful "swan" and Sheldon looked dashing in his tux. For this couple—besides seeing them win a Nobel Prize—seeing them get married was one of the highest moments in their relationship.

MAKEUPS AND BREAKUPS CAN DO SOME GOOD

Sheldon buys Amy a tiara

In "The Commitment Determination," the gang is shocked when Amy breaks up with Sheldon. After spending five years together, Amy had enough of Sheldon's lollygagging. He didn't appear to take their relationship seriously and cared about Star Wars than about their relationship.

RELATED: Big Bang Theory: The IQs Of The Main Characters

Amy decided to go on a break from Sheldon but he suffocated her decision, making her end it all. Personally, it was because of this breakup that made them as strong as they were in the 12th season.

WHEN THEY FIRST MOVED IN TOGETHER

SHELDON AND AMY MOVE IN TOGETHER - TBBT

With water damage ruining Amy's apartment, she uses this time out of her space to create a new one with Sheldon. The two decided to run an experiment to see how well they could happily live together. Amy was enjoying her one-on-one time with Sheldon so much that she lied to him about the reality of her apartment. Her apartment was ready for weeks before Sheldon caught her in the lie. However, it proves that these two could happily and safely live together as a couple. A huge move for Shelly, since he wasn't in his own space and he had a new roommate!

COITUS, COITUS, COITUS!

Once Sheldon and Amy got back together, it was just in time for Amy's birthday. In a present to trump all presents, Sheldon decides to gift Amy his "genitals." Going all the way was a big deal for the pair as it was both of their first times (and the most physical they've ever been with one another).

RELATED: 10 Continuity Errors That Fans Probably Didn't Notice In The Big Bang Theory

The two took baby steps but by the end of their love-making, it was clear both were quite happy with how it went. Sheldon even joked (but it wasn't a joke...) that the next time they would make love would be in a year on her birthday again.

THEY ACHIEVED A NOBEL PRIZE AS A UNIT

Amy and Sheldon giving speech at Nobel Ceremony

Sheldon and Amy have two of the most brilliant minds on the show. Together, they are even stronger. In "The Confirmation Polarization," it becomes clear that Amy and Sheldon have a high chance of winning a Nobel Prize. Later in "The Change Constant," Amy learns that she and Sheldon won the Nobel Prize and we see them happily accept their huge honor in front of their closest friends. Seeing each other shine in their respective fields was one of the most beautiful moments in their relationship.

AMY WAS THE FIRST WOMAN TO MEET MEMAW

After first meeting Sheldon, it's very clear that he has a close connection to both his mom and memaw. Mary Cooper is very understanding of how smart her son is and realizes that Amy Farrah Fowler may be his only real chance at happiness with another human being. But winning Sheldon's mom's heart wasn't the issue, it was winning his memaw's heart. Amy is the first girl to meet his memaw and was also the first girl to break up with Sheldon — something his memaw did not appreciate. The two eventually hashed it out and realized that they both just wanted what was best for Sheldon.

WHEN THEY CREATED A CELL BABY

Around the time Bernadette was pregnant with Halley, Amy and Sheldon mixed their own DNA to create a superhuman in cell form. After realizing that their cells were high functioning, Sheldon had a "profound" sense of creation. He then wanted to make a baby with Amy immediately, in hopes of creating even smarter human beings. Procreating wasn't in the cards for this couple during their time on TBBT, so seeing their mixed DNA cells was the most we'll ever get from these two.

NEXT: Big Bang Theory: 10 Reasons Why Sheldon And Howard Aren’t Real Friends