Penny admits she fears Leonard will leave her for someone smarter. They eventually agree to stop worrying and focus on their new marriage. Sheldon’s Retaliation
In the second episode of Season 9, " The Separation Oscillation ," the aftermath of Leonard and Penny’s elopement and Sheldon and Amy’s breakup takes center stage. Leonard and Penny’s Conflict
Dealing with the breakup, Sheldon attempts to hurt Amy through his web series, "Fun with Flags". The Big Bang Theory recap: The Separation Oscillation
The episode begins with Leonard having a nightmare where he kisses Sheldon to "restore balance" to his marriage after admitting he kissed another woman, Mandy Chow.
Mandy dismisses his concerns, leading Leonard to realize he subconsciously tried to sabotage his marriage because he feels he doesn't deserve Penny.