This for some general advice on romance stories. For the exposition, they could have a project together in one of their classes, and they become friends. Since you mentioned Halloween, while they work, the blind girl could tell him about a dream she always had—winning a costume contest at the Halloween dance. The loner could help her out since she can’t see the costumes but can come up with ideas since she wasn’t always blind. If you go with that, you could have them win another contest together, like prom king and queen, if they end up as a couple.
My biggest advice is to make sure the loner’s only personality trait isn’t just being a loner or a loser, and the blind girl’s main trait isn’t just her blindness. Characters who focus on one trait tend to make terrible stories, especially in romance. They feel like plot devices rather than actual people. Also, if it’s from the perspective of the blind girl, be sure to include lots of sensory details. While she can’t see, she can still hear, feel, and smell. And don’t rush the dating part either. It should feel natural—rushing isn’t a good idea in real life, so why would it make a good story? For just writing advice, read the helpful articles older members of the site have written, like
this,
this, or
this. If you do join the contest, good luck, and have a great time while you're around.