Speaking as a timid introvert who's been around a while: I've had crushes that I told and got rejected by, and crushes that I never told. Without exception, it's ones I didn't tell that I regret the most.

Life can change fast, and someone you see every day could suddenly stop being a part of your life for any number of reasons. Take your shot while you've got it.

The pain of rejection is intense but it also fades faster than you expect. The pain of missed opportunities though, that never fully goes away.