Technically not exactly unrequited love, but "If I Can't Love Her," from Beauty and the Beast. It's really about the Beast wishing he knew HOW to love, but it's the same general feeling.
Also, "Where's The Girl" from Scarlet Pimpernel, which is technically about EX-love.
In my pants, she has burst like the music of angels, the light of the sun! --Marius Pantsmercy