Of COURSE there's a fancy word for the intensity of an obsessive crush!
Coined by Dorothy Tennov in 1979, Limerence is a noun which refers to the state of being (more or less involuntarily) infatuated or obsessed with someone and is characterized by a strong desire for reciprocated romantic feelings.
Limerence is really that fixation stage during which a person over-analyzes everything their crush says or does, looking for meaning. Like the internal monologue of "Oh my god, they were listening to (x) song, and I looked up the lyrics, and it COULD be about me, but maybe it's not, do they hate me? Did they notice that I did (x) today because I heard they like that too..." except with dramatic swings between euphoria and despair.
The key with limerence, though, is the unattainability. Minor positives reinforce the attraction (without offering any fulfillment) and people can experience the state of limerence for weeks, months, or years. It's generally not a great thing... though it is incredibly common.
Here's hoping you can avoid it if possible, or identify it and work on it if you can't!
Good luck,
-C