Wiktionary
n. Love that is not reciprocated, even though reciprocation is desired.
Wikipedia
Unrequited love or one-sided love is love that is not openly reciprocated or understood as such by the beloved. The beloved may not be aware of the admirer's deep and strong romantic affection, or may consciously reject it. The Merriam Webster Online Dictionary defines unrequited as "not reciprocated or returned in kind."
Psychiatrist Eric Berne states in his book Sex in Human Loving that "Some say that one-sided love is better than none, but like half a loaf of bread, it is likely to grow hard and moldy sooner." Others, however, like the philosopher Friedrich Nietzsche, considered that "indispensable...to the lover is his unrequited love, which he would at no price relinquish for a state of indifference." It can also be contrasted with redamancy or the act of reciprocal love.
Usage examples of "unrequited love".
So what is this thing you have about tall women and unrequited love?
If the answer is bad, well, among my species unrequited love is a serious condition but it is rarely fatal….
The poem was a song of unrequited love, filled with dark imagery and sensual innuendo.
The music flowed into space, unrequited love, bound-less passion unanswered.
We spend our working time plotting, killing, being raped, deserted, murdered and/or suffering the pangs of unrequited love, so is it any wonder we’.