10 Big Man on Hippocampus

Peter gets in a fight and hits his head, causing him to suffer from amnesia. This causes him to forget everything about his life, including his family. Lois decides to reintroduce Peter to his old self, including his sex life, in an attempt to jog his memory. Later, Peter mistakenly believes himself free to have sexual relations with other women. Deeply angered, Lois and the rest of the family decide to move out and leave Peter. Quagmire takes the opportunity to finally pursue a relationship with Lois. When Peter returns home later that night, Brian warns him about this development, and Peter reveals that he finally regained his memory. He then rushes to reclaim Lois, while Quagmire's plans had been stymied by guilt-induced impotence.