Love is an important motivation in real life and in traditional fiction, but often gets short shrift in roleplaying games behind other, more self-focused, motivations such as greed and powerlust and the quest for better equipment.
So as a GM you can mess with your players' heads by having an NPC motivated purely by love for another person, sacrificing everything else in their yearning for true love. And as a player you can seriously mess with your GM's head by doing the same thing.
Darth Vader: I loved you, Anakin. I still love you.
Luke: How can you love him? He's a monster.
Darth Vader: Yes, he's a monster, but I still love him. Love is unconditional, my son.
Darth Vader: I still cherish the memory of the kind boy who gave me the Japor snippet.
Anakin's Voice: That trinket? Meaningless!
Darth Vader: You've forgotten what is truly important.
Anakin's Voice: Power is all that's important. Dominance! It doesn't matter how.
Anakin's Voice: The Emperor understands.
Palpatine: I have seen the dark universe yawning; Where the black planets roll without aim.
Palpatine: All I ever wanted... was to bring peace to the Galaxy.
Luke: Yeah, one Peace Moon at a time.