How does a married person affect the relationship of both singles?

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I have a friend who ask an advice from me. She told me that she has a married neighbor who kept on courting on her. She told me that the guy has been sending text messages to her during midnight asking for her to go out from their house. She's afraid so she did not go out. She's been doing things just for that married guy to stop courting her. She had said bad words to that guy, but sad to say the guy did not stop. My friend don't know already what to do so she told her boyfriend about it. Her boyfriend said to just stay away from that guy. Then one day her boyfriend visited her at their house. When her boyfriend went home, the married guy saw her boyfriend and get angry. He followed to my friend's boyfriend so my friend try to stop her neighbor. Her boyfriend has went away. A day after, the guy kept sending messages to her discriminating her boyfriend and wanted to be chosen by my friend. What could you say or advice? Please help me help her. My friend doesn't want to be the reason that the couple would be separated. And she doesn't want to be in prison.