Among The Big Bang Theory’s many relationship arcs, Leonard’s cheating remains one of the most controversial. He admits to kissing another woman while in a long-distance relationship with Penny, but the consequences feel surprisingly mild. Penny is hurt—but the relationship survives. For some viewers, this felt unfair, especially given how often Penny was criticized for her own flaws. Others saw it as intentional realism: not all cheating leads to dramatic endings. The writers framed Leonard’s mistake as emotional weakness rather than malice, forcing fans to decide for themselves how serious it really was. That ambiguity is exactly why the storyline still sparks arguments long after the series finale.