Rachel Berry has three things going for her in the world, and three things alone. The first is the obvious: she can sing. And man, can she sing. But that's not the point – everyone knows that one front and back already. Rachel Berry can sing, and she's pretty damn good at it. The second is that she can cry on cue. In the summer of her third grade year, way back when, after she realized that she was oh-so-destined for Broadway, she made it a critical study to figure out how to cry on cue. It took her two months and countless onions, but whenever she thinks of slicing onions, and the feel of a knife in her hand, the tears come. It's a talent. Of course, it also posed problems when they had to eat all the onions that she went through, but Rachel Berry is also an excellent cook. But cooking isn't going to get her all that far in this world – didn't her "I'm sorry" cookies go uneaten?
But anyways, Rachel Berry has three things that equip her against the tide that threatens to drown her rising star. The first two are talents, be it God-given or acquired, but the third one is one that she has an incredible sense of the romantic. This probably comes from one of her fathers, and it probably comes a bit from her mother, and it probably (just a leetle bit) comes from all of the old movies that she watched while growing up, the musicals, the classics, and –most importantly – all the books. She grew up in novels of lust and love and betrayal and tumultuous happiness, and has a small – oh so tiny! – bit of a hopeless romantic in her. That's why she was so keen on Finn Hudson at the very beginning of things. Hello? Of course it was destined to happen. He'd not only be her ride to popularity, but maybe even her ride to the adult world. (And to school, because her fathers were getting annoyed with her elaborate morning routines.)
She's a singer and a sobber and she is just talented as anything, so when Finn has a baby on the way, and she realizes that he's far more pain than she can ever deal with, she's emotionally vulnerable. Fragile, if you will, the sort of fragile that people stamp "handle with care." It's a just-right kind of fragile that lets her wallow in her despair, but still remain functional enough to realize that Jesse St. James is not only the lead male of Vocal Adrenaline, he's also a heartbreaker and undeniably good looking.
So when he breaks her heart all those weeks later, his eyes so unbearably sad in the middle of his caring bad-boy routine that's stolen her heart, it's all that she can do to keep herself from slumping down then and there at her locker and breaking down to cry. When he walks away, she doesn't think so much of I have been too much in the sun as perhaps I should've learned how to faint on cue. If she fainted, he'd have to rescue her. Someone would – she's Rachel Berry, and a girl, to boot. Even if this is the last stand of civilization against the encroaching fields of barbarism, at least someone would have to catch her. She'd be in strong (hopefully masculine) arms, and then Jesse would have to turn around and see what caused the commotion and why he wasn't at the center of it all. In the moment where she feels like she should be breaking down and sobbing like an idiot, nothing happens. No earthquakes, no horses eating each other, nothing. Only her, and the small bit of an idea that's her lifeline, because there's still something she has to do in this world.
Her heart is breaking. It is broken; she knows that much for certain. But the one thought in her head when he walks away is perhaps I should've learned to faint on cue.