In "Brian in Love" Meg finds a pee stain in the carpet and thinks Stewie did it. Later that night Brian who has really been doing it does it again and blames it on Stewie. Since they think Stewie has been having the "accidents" Peter goes to pick up some potty training books. Then when they go to the supermarket Brian ha another "Accident" and this time everyone saw it.
Stewie starts causing more trouble for Brian by peeing all over the place and blaming "Patches"(Brian). After Peter mentions being an outside Dog and Lois mentions getting him fixed, Brian goes to get help. Brian admits he loves Lois and is told to confront her so he does but, Lois rejects him.