Two people who are highly sexually attracted to eachother, and who find themselves longing for their sexual partner throughout the day. And cannot stay alone with eachother for very long without sexual interaction. And for other reasons unknown these two people decide to keep their relationship in the boundaries of "fuck buddy".
Joe : dam sasha is hot, do you really fuck every time you hang out with her?
Bob : hell yea
Joe : dam you guys make a good couple when you going to start dating?
Bob : we aren't , we're just soul fuck buddys
Joe : you lucky ass.