heartbreaker

Short definition from Wiktionary

Noun

1. 1
   Someone or something that breaks someone's heart, as: A person, usually attractive, who flirts with or otherwise enamours another person, but does not reciprocate their love.
2. 2
   Someone or something that breaks someone's heart, as: Something that causes sorrow, grief or extreme disappointment.
3. 3
   Someone or something that breaks someone's heart, as: A match which ends in defeat for a promising player or team.
4. 4
   Someone or something that breaks someone's heart, as: A curl or lovelock.