Feelings I had for my classmate were obviously one-sided (pretty sure of it), so I made a reasonable decision to never confess to not make things awkward. In a few years since we graduated I finally moved on, although I never loved anyone this much since.
Yet all this time I had a desire to tell her about them. I would definitely want to know if someone loved me this much ever. Would she? I don’t know. I don’t even know if she is in a relationship right now or not.
I would really want to cite some scientific study that “Over 80% of girls have their self-confidence lifted after being told they were secretly admired (p<0.05)”, but can’t find one.
The only time I have told someone about feelings I had long ago is when we started hanging out again and they were open to reciprocate. Not an out of the blue cold call.
To be clear, in this context NOT telling them would be the wrong decision. Very, different from OPs situation.