Lovesick (adjective)

1. Miserable because of unrequited or lost love.
2. Feeling sad, depressed, or lovesick as a result of unrequited love or the loss of a loved one.

Origin:

Compound word of "love" and "sick".

Examples:

1. He was lovesick for the woman who had left him.
2. She was lovesick and couldn't eat or sleep.
3. The lovesick poet wrote sad and melancholic verses.
4. The lovesick student was unable to concentrate on his studies.
5. The lovesick person's behavior became increasingly erratic and irrational.