Canon divergence in season 2, after the locker Room scene. Kurtofsky happen after the kiss, the bullying stop and Kurt goes to New York with New Direction as canon but lose at Nationals. The Chandler debacle did happen but David just asks nicely Chandler to back off.

Then, when the couple goes to NYC, Kurt is attending Nyada and David is working as a bouncer in a club. A quite fancy one, thank you. Here, he meets Blaine who is performing time from time while Kurt runs into Sebastián more than one time in this coffee shop between Nyada and Nyu. And then one night, the four men meets at dinner, and Kurtofsky get to know those two handsome men, apparently also coming from Ohio, Westerville. Kurt slowly aknowledges them once they mention The Warblers, from Dalton and then recall some memories with Blaine, whom he did have a talk with. One thing leading to another, they start hanging out.

They try at first swapping partner. Sébastien and Kurt banter and snark like an old couple while being all cheesy and cute with Blaine. David being not the open one could just chat lightly with Blaine who is friendly with everyone and tries as hard as he can to not punch Sébastien who tends to cross the line. At least the sex is hot. 

They later find out their are eache other soulmate's.