It's morally unacceptable to manipulate another person.
Alan's girlfriend Jessica has a best friend, Kary, who Alan finds very annoying.
Alan wants to deal with Kary's annoying tendencies.
Alan tries to limit his time with Kary and encourages Jessica and Kary to hang out together without him.
Alan convinces Jessica that Kary doesn’t value her as a friend and is only using her to get free food and drinks, for which Alan has no evidence.
Jessica and Kary continue to be best friends, and Alan doesn't have to deal with Kary so much.
Jessica cuts Kary out of her life and stops trusting anyone but Alan.