No matter how much TV tries to normalize it, there's never an excuse for cheating on your partner.
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Whether the couple ended things or not, the relationship became tainted the moment the trust was broken between them.
We created a slideshow below of 19 relationships that were ruined by infidelity.
1. Callie and Arizona - Grey's Anatomy
Callie had stood by Arizona's side through everything. Callie gave up so much to support her and attend to her needs after the plane crash. We feel for Arizona, but we don't sympathize with her decision to hurt her wife.
2. Finn and Quinn - Glee
Not only did Quinn cheat on Finn, but she convinced him that even though they had never had sex, he was the father of her child. Talk about lies and betrayal.
3. Ethan and Emma - The Lying Game
Ethan and Emma were already starting to lose their magic, but Ethan's kiss with Sutton sealed the deal. Was anyone else shipping Emma and Thayer at this point?
4. Barney and Nora - How I Met Your Mother
Barney and Nora weren't a main relationship in the series, but they did have great potential. It almost seemed as if Barney was a changed man when they were together, but he cheated on her with Robin and told Nora the truth while he was meeting her parents.
5. Piper and Larry - Orange is the New Black
When Piper went to jail she was still engaged to Larry, and the two planned on being together once she got out. But Piper cheated on Larry with her former flame, Alex, and Larry put an end to their relationship.
6. Josh and Liza - Younger
Team Josh all the way. The biggest problem in this relationship was Liza's lies and manipulations. Josh was able to look past everything she had done to him because he loved her so much. But it's got to hurt when you plan out an elaborate proposal only to see your girlfriend kissing someone else before you can get down on one knee.