It's wrong to sleep with your siblings significant other
Josh is watching television with his brother and his brother's girlfriend, just before his brother needs to leave for work.
Josh wants to find a partner for himself.
Josh decides to create a profile on a dating site to meet someone new.
Josh tries to sleep with his brother's girlfriend, as soon as he finds himself alone with her.
He meets someone who he really likes, and they all start to enjoy double dating and social evenings together.
She calls his brother to complain about his behavior, embarrassing Josh and hurting his brother's feelings.