Sad and lonely because someone you love doesn't love you back or is unavailable.
From 'love' plus 'lorn' (archaic past participle of 'lose,' meaning bereft or abandoned). This romantic word reached peak popularity in Victorian literature.
This word is almost always used ironically now because it sounds so melodramatic—it captures that deliberately overwrought heartbreak feeling that makes us both cringe and sympathize with lovesick characters.
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