Jenna believes that Migo, his husband, cheated on her. So she did That Mistake. She told to Migo that she's the one who cheated. She don't want to pity herself. That's why she did that Mistake.
When Paula comes back from her business trip, she finds her husband and her best friend in her house . All along she thought that she was just over exaggerating when she thought the two had something going on. She thinks back to all the events that caused the betrayal, and she soon realizes that there was more to the story than what she assumed .