Spoiler Speculation under the cut
Ok, so what if Kurt’s questionable behaviour is him distancing himself from Blaine? Like maybe Kurt talks to Burt and Burt asks him what he’s going to do about Blaine next year, which sparks Kurt’s thought process about how they’ll be far apart and maybe it would just be easier to end the relationship before it goes completely and utterly sour.
So, Kurt starts keeping himself away from Blaine, not hanging out with him as often as he used to, and Blaine starts to get upset because what could he have possibly done to make Kurt do this and he sings the Whitney number because he’s getting all emotional about Kurt leaving and how Kurt’s being irrational.
Then we have the scene in Emma’s office where Kurt and Blaine talk it out with her (much like the scene in season 2 where Finn and Rachel go to Emma about the whole Santana-Finn sex issue, but that ended pretty badly. Hopefully it’d end better for Kurt and Blaine) and Kurt realizes he’s being irrational and their love is strong enough to make the distance and he sings the love song and BAM life is good again.