This is set during Laryngitis during Season 1 (episode 18). I was re-watching Season 1 and this jumped out at me!
Santana was bored, and applying her make up during Glee. She was more worried about her make-up that might have gotten blotched in the hallway than whatever lame songs someone was singing.
And then she heard Kurt ask to sing. She rolled her eyes, ready for some girly sounding song, that was in his usual repertoire. So she tuned it out.
Hmmm it looks like her left eye was not as even as her right eye, she better fix that…than all of the sudden she realized Kurt was singing a Mellencamp song of all things.
What. The. Hell.
She gaped up at him, totally shocked by this odd song selection from Kurt. Oddly, she felt herself fighting back tears. She realized what Kurt was doing, he was hiding from who he truly is, just as she has been hiding, for a few years now.
Santana wanted to jump up and stop the song and tell Kurt to be proud of whom he is. She couldn't. That was not part of this façade that she has worked so hard to create. She made a mental note to herself to try to figure out some way to approach Kurt after Glee.
As Kurt finished singing and walked away, Santana tried to get all her make-up put away quickly, bending over her bag.
When she stood up, she realized someone was already talking to Kurt. Brittany. Her Britt-Britt. She knew the look in Britt's eyes. She had seen it before Britt put a move on a football player.
No way. She couldn't be making a move on Kurt. Santana felt glued to the floor. She wanted to walk over to them, grab Brittany and kiss her, and mark her as her territory. She was sure most of Glee had already figured out their relationship, after the whole "If sex were dating…" line.
She couldn't. Her façade would be crumbled. The slushies would come, but worse of all the names. She couldn't handle it, and she knew Brittany couldn't.
She was stuck.