The reason a MIL doesn't like the SIL and the reason a friend would tell a spouse to leave their spouse is for ONE REASON..
It is YOUR SPOUSE that is feeding the friend negative information about you to her friend. That is how it works. That is why she has an bad opinion of you and not know you. Your wife is feeding her the bad things she thinks of you. She is complaining about YOU to her friend. The friend then forms a bad opinion on you because of the information she has been given. It isn't rocket science...
You need to place the blame squarely on the culprit. YOUR WIFE. Why would your wife be talking badly and telling her friend rotten things about you? What is going on there? Any truth in it?
You are dancing all around the real issue here. YOUR WIFE. and what she is feeding the friends for information. If she was telling them you were the best thing that ever walked the face of the earth, her friend wouldn't have a chance in hell in convinncing your wife to leave you and wouldn't even bring that up.