I'm considering writing about a person I've had a crush on for the past several years. Is this a bad idea?

The topic you choose should shed some light on why you would be a valuable addition to the student body. Even if your crush is relevant, I think you could probably find another subject that would do more to convey your strengths. As difficult as it is to judge your own admissions essay, the task becomes even more difficult when writing about love. You risk being too sentimental and melodramatic.