Why is this woman obsesses with me and my husband? Why is she trying to break us up?

[raspyaftermath967]

This crazy woman has been harassing me online, sending me messages saying that my husband is with her and they are in love. He denies ever being with her? I have asked him many times and he has said no every time. He even got upset because he says that he doesn't know why I am falling for this trick's antics. I am not about a man calling a woman names but she is the type to always post pics on facebook to get the mens attention. I decided to distance myself from him and this situation but something is bothering me about it. She does seem crazy and no one likes to be constantly accused of wrongdoing. I don't know what to do. She has stopped with the harassment for a few days now. Could she be doing this because he cheated or because she wants him so she feels the need to break us up to do it? By the way she says that she knows we are married but doesn't care because they are together.