((YOU! why could you...*is jealous that he hadn't thought of that wording*))
Every time you think someone looks half decent to you, they instantly fall obsessively in love with you, killing all competition and not taking no from you as an acceptable answer. as a result, most of the population except the winner dies. Once the winner is mutilated by combat, you find them less attractive, and the feelings disappear. Over time this drives you to loneliness, and you lower your standards, killing more people each time you do, but never having a meaningful relationship for the rest of your life.