Why do I have this annoying tendency to overthink and worry about everything?

Just can't stop thinking about my crush, who I kissed on the last Friday before finals week. I really like him and really hope something will come of it once school starts back up. But I'm so worried that I'll just get hurt again and get my hopes up for a whole bunch of nothing.
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"The rain keeps crawling down the glass. The good times never seem to last. Close your eyes and let the thought pass."
'Prodigal' by Porcupine Tree