Typically a high school girl. Somebody that throws their life away completely into a relationship, usually in high school, that abandons all friends and any other attachment that they had before with anything else in life, for that relationship. If it ends, they usually have nothing to go back on after it ends, due to loss of everything during the relationship. They are the bane of all good happiness in life and will destroy all of your friendships.
Jake: Bro Rachel is so nice to me. I'm taking her on a date tonight!
Joe: Watch out for that Jake, she's a relationship whore...her last boyfriend committed suicide