That first gif is such an “You’re doing this here? Really, Blaine? Really?” expression. He can’t believe that Blaine has dedicated a song to those who’ve been cheated on and he’s singing it and God, you can tell he doesn’t understand what right Blaine has to pull a stunt like this.
The second one is just after the line about getting home after 3am. Santana in the background glances at him while Kurt just shakes his head because Blaine is completely blowing this out of proportion. He’s not cheating. He’s not having an affair. He’s been ambushed in the choir room via song and he’s mad with Blaine because Blaine hasn’t listened to him at all.
The third one he’s getting accusing glances from everywhere. He’s still mad with Blaine but he’s mad with everyone else for turning on him. He’s obviously defensive, shaking his head because he just can’t believe Blaine is doing this. Suddenly this has gone from a fight between the two of them to everyone in Glee club turning on him too. He’s drawn into himself, crossing his arms, and his superior, disbelieving look has been replaced by frustration that everyone is just staring at him with their various expressions which are just so accusing. Everyone thinks Blaine is in the right, everyone thinks Blaine has done the wrong thing, but I wonder if any of them actually knew what was truly going on? (Not that Kurt isn’t guilty in some aspects, but Blaine’s song was pretty vicious)
And the final gif…Blaine’s just walked out and Kurt probably saw the look on his face a split second before he turned and walked out. He can see the way Blaine’s shoulders have slumped, the way his feet are dragging. He knows what Blaine looks like when he’s upset and he’s on the verge of crying, and finally Kurt realises that he did that. He still doesn’t understand what he did wrong, because to him the texts mean nothing, but he realises that Blaine isn’t just mad. He’s hurt. He’s really hurt. He’s upset. He’s crying. And he’s felt so distant from Blaine for so long and he just wants to run after Blaine but he knows he can’t. He knows Blaine has just let his emotions go and now he needs to take some time to breathe through them because he’s seen Blaine angry and hurt and crowded and he just ends up snapping insults that don’t hurt but aren’t shielded by Blaine’s desperate need for approval. And now that he’s realised it, he wants to make it right. He wants to fix it. But he doesn’t know how.
For most of you, these next few weeks will be your last here at McKinley. Lots of changes coming up. Lots of… saying goodbye. To your friends, to your significant others.