There were two options, as far as Kurt could see. Two frameworks from which this whole cheating debacle could be viewed.
The first was one in which Kurt didn't need Blaine. Blaine had been fun, while he had lasted—more than fun, if he was being completely honest. Blaine had been able to relate to him on a level that no one else had—not Rachel, not Mercedes. Not even his dad. But their relationship had run its course, and Kurt was bigger and better than Blaine and what Blaine did to him, and it was over. Yes, they could potentially still be 'just friends', but even that thought made Kurt roll his eyes. He and Blaine had never been just friends. Even now the residuals of their past relationship clogged Kurt's brain, tinged their conversations, woke Kurt up at night. No, ending a relationship with Blaine meant ending all relationships with Blaine. Kurt would cut Blaine out.
The second was one in which Blaine was Kurt's.
Yes, Blaine had done a terrible, terrible thing and hurt Kurt like he never wanted to be hurt again, but he was Kurt's. Unquestionably. By default. Like a puppy that runs away or chews up your best pair of shoes. Okay, Kurt felt a little guilty for comparing Blaine to a puppy, but it wasn't his fault the metaphor was so appropriate. Past all of his affable charm and seemingly effortless achievement, Blaine was a weird, perpetually excited goofball. Sometimes Kurt just got so tired watching Blaine flit between projects and rehearsal and friends and spending time with him.
So, they had tried the friend thing, and Kurt new that wasn't going to last. He wasn't surprised when Blaine asked him to be boyfriends again. He wasn't surprised that Blaine proposed to him. He had been expecting both—he knew Blaine. He had seen the look in Blaine's eyes, the smile that had curled his lips that he had tried to hide, the way his eyes had widened innocently whenever Kurt asked him what he was grinning about.
Yet Kurt hadn't entirely decided which framework he was living from. Yes, his actions had accorded with the second framework, but that didn't mean he entirely approved of them. His dad's illness had meant that he had been really willing to fall into Blaine's support again. Even when his dad was determined to be miraculously clear of cancer, Blaine's wide-eyed earnestness had always been hard for Kurt to resist. But, in the back of his mind, he was still holding on to the sentiments of the first viewpoint. He didn't need Blaine. He could end this thing, and crush Blaine's heart the way Blaine crushed his, at any time. Those thoughts were particularly potent whenever he caught someone checking Blaine out—which happened often, though Blaine didn't notice.
So Kurt wasn't surprised by Blaine's proposal, though he had been surprised by the sheer magnitude of what Blaine had managed to put together. And as Rachel led him through Dalton's hallways, and while rose petals fluttered down on his perfectly styled hair, and while various Ohio high school show choirs led by Blaine, of course, belted out that all Kurt needed was love, Kurt thought about the two frameworks. He really, really did. And he realized that the first choice didn't even make sense.
Because Blaine was his, and it wasn't a matter of how or why, but when. Because he would have proposed to Blaine in a year, or two, or three if Blaine hadn't been such an eager beaver and beat him to it (and Blaine would have gotten a silly grin on his face and looked at him with his stupidly earnest eyes, and would have breathed Kurt, in the way that he did). Because Blaine knew that they were inevitable just like Kurt did. Because Blaine also knew Kurt; he knew that Kurt liked romance and grand spectacles, and wanted to be wooed, and that Kurt wouldn't propose now, it wasn't practical. Because they were still so young. Because of college, and Blaine was still in high school, and the fact that they just got back together. Because of logic. Even though Kurt proposing to Blaine was an inevitability, Blaine proposing to Kurt was a gift. And Kurt didn't know if Blaine just knew him that well, or if Blaine had really good intuition, or if Blaine was just a really good guesser, but either way: Blaine proposed when Kurt wouldn't—when they were still young and freshly heeled and when everything seemed possible but nothing was certain.
And it wasn't perfect. But it was close.