Here is how Dr. Sheldon Cooper—B.S., M.S., M.A., Ph.D., Sc.D., theoretical physicist, lovable mega-nerd—first tells his girlfriend that he loves her. “There’s no denying I have feelings for you that can’t be explained in any other way,” he says. “I briefly considered that I had a brain parasite, but that seems even more far-fetched. The only conclusion was love.”

This confession is so shocking, coming from Sheldon, that the girlfriend in question—Dr. Amy Farrah Fowler, Ph.D.—proceeds to have a panic attack. Amy tries to lie down on Sheldon’s bed to recover, until she is reminded that “whoa, whoa, whoa, just because I love you doesn’t mean girls are allowed in my room.”

The primary romance of The Big Bang Theory, which for a long time has been the most popular comedy on TV, is the one the show established during its pilot episode: the one between Dr. Leonard Hofstadter (Ph.D., experimental physicist) and his neighbor, Penny (aspiring actress, waitress at The Cheesecake Factory). The most compelling romance of The Big Bang Theory, though, has been the one that is a romance only in the strictest and/or most lenient sense of the term: the relationship between Amy and the brilliant, misanthropic, narcissistic, routine-dependent, empathy-challenged Sheldon. The relationship that strains the standard sitcomic formula—unchanging characters in a changing environment—and that, in the process, adds literary dimensions to a show that is otherwise delightful fluff.

And so: While CBS advertised last night’s episode, the season nine premiere, as featuring the eight-years-in-the-making marriage of Leonard and Penny (spoiler: It did!), the focus of the show ended up being Sheldon and Amy. Who ended the previous season deciding to go on a break that might have also been—these things are always a little unclear—a breakup.

The trouble came after Amy lost patience with the core dynamic of their extremely slow-moving relationship: her wanting more, and Sheldon resisting, and their settling on some mutually satisfactory, and also mutually frustrating, compromise. Sheldon has been playing The Game, basically, but entirely unintentionally. Amy, for her part, has put up with this, not just because “your personality quirks, which others find abhorrent or rage-inducing, I find cute as a button,” but also because she hopes, against all reason, that Sheldon will eventually come around. To sex, to intimacy, to something that resembles the image Amy holds in her mind of what romance is supposed to be.

Late last season, the couple—on the “date night” stipulated by the “relationship agreement” Sheldon has required—decide to build a blanket fort in Sheldon’s living room. (“I’ll get the blankets,” Sheldon squeals, “you Google how to have childlike fun!”) Amy decides to take advantage of the opportunity. They’re having so much fun, she points out, and it’s a shame to let a good blanket fort go to waste. So “I could stay really late, and sleep over,” she suggests.

Sheldon: That’s a big step.

Amy: It’s a big fort.

Sheldon: Very well. I will agree to a family-friendly, G-rated, boy-girl sleepover.

Amy: PG: Some scenes may be too intense for younger viewers.

Sheldon: G-Rated, with a warning for families with babies and toddlers.

Amy: You’ve got yourself a sleepover.

The last few episodes of The Big Bang Theory, however, found Amy quickly losing patience with this steady-but-extremely-slow state of affairs. At the end of the season eight finale, the neurobiologist—frustrated in pretty much every way possible—finally had enough. She told Sheldon she needed time away from him. Time to “think.” Genius is not required to know what that means.

What Amy didn’t know, though, was that the thing that for so long seemed impossible—to her, to us, probably to Sheldon himself—was that Sheldon had been planning to propose to her. “Well, Gollum, you’re an expert on rings,” he tells his beloved doll at the end of the episode, taking a small box from his desk drawer. “What do I do with this one?”

The show’s season nine premiere doesn’t answer that question, but it does answer another, more interesting one: What happens when a man with an IQ of 187—a man who understands social conventions the way most of us understand string theory—gets his heart broken? As it turns out: He acts just like an average person. He wallows and whines. He gets angry, and petty. “Some important new information has come to light,” he tells Leonard: “Women are the worst. I thought it was paper cuts, but I was wrong. No piece of paper has ever cut me this deep.”

This is the stuff, certainly, of terrible rom-com cliché. (You half expect Sheldon to procure a pint of Ben & Jerry’s from the freezer of his perpetually well-stocked apartment, and/or to interrupt Penny during her wedding so that she might provide a long-distance rendition of his favorite soothing song, “Soft Kitty.”) And yet, for Sheldon, this love stuff is the polar opposite of conventional: It is new and weird and unexpected. All this romantic angst, from a character who exhibits signs of both Asperger’s and asexuality! A character who tracks his bowel movements on a spreadsheet he posts on the fridge door! Who dislikes gifts, because he believes that they create an obligation on the part of the gifted! Who is the subject of restraining orders from, among others, Leonard Nimoy, Bill Nye, and Carl Sagan! Who thinks wine is “grape juice that burns”! Who calls it “coitus”!

The show, at first, left open the question of whether Sheldon is truly asexual or whether he simply believes, so deeply that his body has cooperated with him, that sex—like alcohol, like drugs—will compromise the workings of the thing that he values most about himself: his brain. What became clear in recent seasons, though, is that he is interested in sex, in his way. The kisses Amy demands of him as part of their relationship agreement have gone from perfunctory to—well, not quite passionate. But something closer to “pleasant”! Amy—who is almost as brilliant as, and even more stubborn than, he is—has gradually changed Sheldon’s attitude toward intimacy. (“Amy has made me a more affectionate, open-minded person,” he admits at one point. While he means it as criticism, it’s also clear that part of him enjoys the empathy being foisted upon him.)

That goes for “coitus,” too. Sheldon is initially attracted to Amy because at their first meeting, she informs him that, for her, “coitus is off the table.” That changes, though, for both of them. For Amy—who once resorted to faking an illness so Sheldon would rub VapoRub onto her chest, and who quickly realizes that an offer of Yoo-hoo, a favorite drink of Sheldon’s (“the name literally beckons!”), is the best way to get him to come over late at night—it changes more quickly than it does for Sheldon. But as their relationship progresses, Sheldon, too, is coming around. Slowly. Very slowly.

“You guys have been going out for years and haven’t slept together,” Penny points out, trying to explain Amy’s frustration to Sheldon.

“Yeah,” Sheldon retorts. “It’s called foreplay.”

We don’t know, at this point, whether that will turn out to be true, or whether Amy really has had it with VapoRubbing her way to intimacy. What’s remarkable, though, is that the question could be asked in the first place. There’s a chance the robotic Dr. Sheldon Cooper might actually engage in “coitus”! And that’s not the only evolution he has undergone. Sheldon has also taught himself sarcasm. He has taught himself a kind of empathy that extends beyond merely assessing other people’s facial expressions and responding accordingly. He has grown, and changed, and gotten better. He has made himself open to the thing that seemed impossible when the show first started: a relationship that is intimate in all the traditional ways.

He has made himself so open, in fact, that he has allowed himself to get hurt.

That kind of stark transformation may be standard when it comes to prestige dramas and the shows that aspire to be counted among them. It is, however, a relatively rare thing in network sitcoms, whose formulas generally rely on characters who remain reliably constant. It’s the situations that change in the situational comedy; the characters, pretty much, stay the same. That’s part of what makes sitcoms, the McChickens of the TV entertainment menu, so comforting.

Sheldon, though, is an exception to that formula. He has evolved, distinctly. His writers, cleverly, have given him the space to become a different person than the one audiences were introduced to in 2007. And because of that, the past eight seasons of the most popular comedy on television have hosted a kind of elaborate, wacky Bildungsroman.

The Big Bang Theory may not be a good show in any literary or aesthetic or artistic sense of that word. It may traffic in tired stereotypes, and over-rely on recycled jokes, and in general serve, for better or for worse, as a textbook example of the “serviceable sitcom.” With Sheldon, though, the show gets a little bit literary. It offers its audience room for analysis, and interpretation. It gives us a figure in the long tradition of Sherlock and Spock and even Prufrock—characters who are extremely mature in some ways and extremely juvenile in others. Characters who see the world as a series of systems and structures, but who are at their most compelling when they let their own messy humanity shine through.

The Big Bang Theory’s theme song celebrates evolution—of Earth, of humanity, of scientific progress. Its story, though, celebrates evolution on a much smaller scale: the slow change that occurs when people open themselves up to others. The show has been interesting for all these years in large part because Sheldon’s own progress, from vaguely robotic to vaguely romantic, has itself been so interesting. And also because, in some sense, we’re all a little bit Sheldon. We’re all a little bit stubborn. We’re all a little bit selfish. We’re all a little bit genius, and a little bit silly, and a little bit scared. We’re all hesitant. We’re all hopeful. And most of us, after a long day of being all of those things, can appreciate the simple sweetness of a tall, cold glass of Yoo-hoo.