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.
Honestly, if this is something you really want to do, I don’t think it’s a bad idea, but you do need to be careful.
Don’t make it creepy. Don’t use the word “love”. You did not love her, you had a crush on her. Keep it simple. Keep it friendly.
Something like “Hey, (something) just reminded me of you, and I wanted to say hi. I don’t know if you ever realized it, but I had a little crush on you in school. Hope your doing well!”
No romantic poetry, no talk of love or soul mates. You just throw it out there, and let them control the narrative. If they never respond, you never follow up. If you talk as friends, then be friends. If they secretly had a crush on you this whole time and want to get together, congratulations!
Best answer by far, in my opinion.