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.
I think there are a lot of things at play here. Ultimately I don’t think you should, though.
The fact that you still want to tell them is suspicious. I think you’re not being honest with yourself. Your ulterior end game is a hope of some type of reciprocation. You haven’t moved on.
Just because (assuming it’s even true) a statistical model of a gender says “they probably would like it” is irrelevant. Would this individual like to hear it? It sounds like you don’t know. If you don’t know them well enough to anticipate how they would react, then I think it’s pretty safe to say they don’t know you well enough to receive the message “I used to love you” in a way that could ever come out as a net benefit to them.
I empathize immensely regarding your position. But as a 3rd party observer, don’t do it.