They break up the August before Kurt's junior year of college, Blaine's sophomore.
There is no anger or resentment from either of them, just lots of tears. They come to the mutual decision that maybe it's time for them to spend some time apart from each other to figure out who they are without the other (they have been together since they were seventeen, after all). Kurt is going to London for a semester anyway and it was hard enough for them to be ten hours apart from each other that one year, so how much harder is it going to be when they are an ocean apart?
The next morning, Blaine moves out of the apartment he, Kurt, Rachel, and Finn have been sharing for the past two years and into a dorm room on the NYU campus. A week later, Kurt leaves from LaGuardia Airport headed for Heathrow, his heart not as excited for the new adventure as it should be.
The minute he lands, Kurt immediately sends a text to Blaine (I made it. Just landed!) before realizing that they are no longer together. Nevertheless, Blaine's response is almost immediate (That's great. Have fun!). He smiles at his phone and hurries off to retrieve his luggage and find the classmates he came with.
Over the course of the next few weeks, the same thing happens. Kurt sees something he wants to tell Blaine about and instinctively texts him a message or a photo. Blaine always responds, until one day he doesn't. Kurt's not sure how he feels when his phone doesn't light up that first time with an answer, but he chalks it up to Blaine being busy with school.
After a couple days of having no contact with Blaine, Kurt starts getting worried. He sends off a queue of rapid-fire texts to both Rachel and Finn asking if Blaine is okay. Neither Rachel nor Finn responds, but he finally gets a message from Blaine (Can we Skype tonight? I need to talk to you.). Kurt suspects Rachel told Blaine to send the message but he responds nonetheless (Sure. Tonight, 6 your time?). Blaine agrees and it's settled.
When he logs onto Skype that night, Kurt certainly doesn't expect to hear Blaine say that he's been seeing someone for a couple weeks. Kurt's barely looked at any of the guys since he's been in London, despite their fantastic accents. His heart has not forgotten Blaine and he can't bring himself to try and stop loving him. Blaine explains that he didn't go looking for anything, it just kind of happened – kind of like them. He says that this is what their break was supposed to be about, finding out if they really are it for each other. He's not in love with this guy, they've only been on a couple dates. (Yes, he thought he was in love with Jeremiah after one date over coffee, but he knows better now.) After they say goodnight and Blaine promises to still keep in touch with him, Kurt crawls into his bed and cries himself to sleep.
Kurt doesn't send Blaine nearly as many texts any more over the next couple months. He attempts to not think about Blaine with someone else by throwing himself into his classes. Late one night in the middle of November after a very long rehearsal, Kurt finds himself in the apartment of one of his cute, British classmates. They bond over theater and clothes and have a couple drinks. By accident (although the next morning he's not really sure if maybe it wasn't a little on purpose) Kurt ends up locked at the lips with this guy. They make-out for a good ten minutes until things start getting heated and Kurt pulls away. He quickly grabs his coat and keys and runs out, upset.
He doesn't sleep much that night, thinking about what happened on that couch and how wrong it felt because it wasn't Blaine. He cries over Blaine for the first time since their Skype session in early October, thinking of Blaine falling in love with someone else. The next morning he wakes up to a text from Rachel telling him that she had spent the day with Blaine (He's doing well. I think he misses you, though.) Kurt scoffs and throws his phone across his bed without answering, feeling miserable and alone and incredibly homesick.
He starts counting down the days until his classes and finals are done and he can return to New York. He is suddenly sick of London and the attractive boys it houses. He doesn't want to be around them anymore, even if it means having to be around Blaine without being with Blaine. (He knows that once he's back in New York he's inevitably going to seek him out, despite whatever pain it might cause him.)
Once December hits, Kurt starts getting really anxious for the semester to be over. He can't wait to be back in the States for Christmas with Burt, Carole, Rachel, and Finn. He hopes, certainly, that Blaine will spend the day with them, but he's not so sure if he has a new boyfriend and friends.
Finally, the semester is over. He excitedly boards a plane in Heathrow and excitedly disembarks at LaGuardia. He runs the fastest he's ever run when he sees his dad waiting for him at the gate and clings to him tightly, really in need of a hug. He next hugs Carole who gives him a big squeeze and Finn who gives him a big bear hug. Rachel practically knocks him over in her excitement of having him back and the five of them leave the airport, Kurt's heart slightly lighter than it has been in months.
An hour after he's back and settled into the apartment again, Blaine knocks on the door. Rachel lets him in and suddenly the two of them are left alone; Burt, Carole, Rachel, and Finn magically disappeared for lunch somewhere in the city. They stare at each other for a minute before Blaine launches himself at Kurt.
Their lips connect and Kurt, initially surprised, wraps his arms around Blaine's neck and Blaine slides his own around Kurt's waist. The kiss is feverish and sloppy, their tongues battling for dominance. They break apart eventually, both breathless and flushed. Still entwined, they somehow make it to the couch and fall into each other's arms, like puzzles pieces.
Blaine catches Kurt up on what happened with his guy – Kurt does the same – and they both come to the conclusion that it felt completely weird and wrong. Blaine's new guy wasn't Kurt and Kurt's wasn't Blaine. There was no real connection between them, no spark when they kissed the way there is between the two of them. They stop talking and make out again, as if to prove their point. Kurt pushes Blaine down into a lying position and straddles him, pressing wet open-mouthed kisses to his neck.
They stop before things lead to sex though, agreeing to go slow to get things back on track. They spend the next couple hours watching a movie and talking, falling back into the easy rapport they've had with each other for so long. They say all the things they need to hear (I'm so sorry. I love you. You really are the love of my life. Let's never do this again.) and end up falling asleep on the couch, Kurt's head on Blaine's shoulder.
The next morning Blaine moves out of his crummy dorm room and back into the apartment and Kurt's bed.