Jane is Will's girl crush. Or maybe she's not. See, for the first half of the novel, Will can't figure out whether he likes Jane or not. Then she gets back together with her ex-boyfriend and Will suddenly decides that she's the one for him. It's kind of how Will rolls—he doesn't want someone in his life until they're gone.
Anyway, though it takes Will a while to realize, right from the beginning it's clear he's kind of into Jane:
I look at Jane for a long time and a slow smile creeps over her face. Her whole face changes when she smiles—this eyebrow-lifting, perfect-teeth-showing, eye-crinkling smile I've either never seen or never noticed. She becomes pretty so suddenly that it's almost like a magic trick—but it's not like I want her or anything. Not to sound like a jerk, but Jane isn't really my type. Her hair's kinda disastrously curly and she mostly hangs out with guys. My type's a little girlier. And honestly, I don't even like my type of girl that much, let alone other types. Not that I'm asexual—I just find Romance Drama unbearable. (1.82)
Sure, she's not his type, but he finds her attractive and funny and smart and they like the same music. Relationships have been built on worse things. And then Tiny starts to push them together, as is Tiny's way. When Jane tries to kiss Will, though, he panics and tells her that he doesn't like her. This must be pretty darn mortifying for Jane, but to her credit, she's able to just forget about it, even though it's clear she still has a thing for Will.
The turning point in Jane and Will's relationship comes at the Maybe Dead Cats concert. Jane runs into her ex-boyfriend and mistakenly thinks that he's the one who dedicates "Annus Miribalis" to her. While Jane might have the details wrong, she is right about one thing:
"It turns out that he had MDC dedicate a song to me which was the kind of thing that he would never have done before and I feel like I deserve someone who consistently likes me which you kind of don't." (9.41)
Yes, Jane, you do deserve to be with someone who likes you back. You go on with your healthy self-esteem, girl. Will has pretty much brushed Jane off for the last hundred pages at this point, so why should she put her life on hold for him? Jane might like Will, but she's not going to spend the entire book pining over him. If he can't figure out his issues, she'll move on. Turns out, the whole getting-back-together-with-the-ex-boyfriend episode is just the kick in the pants that Will needs.
Jane is pretty much the person who makes Will rethink all his relationship fears. Once he can't have her, he decides that he does like her. Maybe being in love is worth all the heartbreak in the end? We sure hope so. And either way, we're pretty sure that Jane has what it takes to peel her broken-hearted self off the floor and get on with her life.