Issues with future mother-in-law and fiancé. Am I in the wrong here? Need honest advice please?

I used to have a very close relationship with my mother-in-law, but with time I've realized more and more that she has a shady and unpleasant character. She would oftentimes make racist, judgmental remarks. She's an older lady so I've tried to let some things slide, but I found out that behind my back... show more I used to have a very close relationship with my mother-in-law, but with time I've realized more and more that she has a shady and unpleasant character. She would oftentimes make racist, judgmental remarks. She's an older lady so I've tried to let some things slide, but I found out that behind my back she was saying she didn't really accept me for her son because I come from a different cultural background. When I confronted her about this, she began talking in circles and didn't even apologize or try to amend. To make matters worst, she's made inappropriate comments to me regarding my fiancé's past relationship. She would tell me what a wonderful person she was and how her and my fiancé still have and will always have a strong bond and connection. I finally had to put my foot down and tell her that I don't ever want to hear about his ex again, because it makes me extremely uncomfortable and is just not ok with me. She said she understood, but obviously did not. The other day I went to visit her in an attempt to be nice, and she had a guest over. While I was sitting RIGHT THERE, she starts telling her guest how her son used to live with his ex who was such a nice girl and mentioning other unnecessary things about it in my presence. I promptly grabbed my bag and made an excuse to leave. I came home and told my fiancé what happened and that I never intend to see her again. Well, she wrote me an onslaught of messages afterwards both to him and I.
Update: Saying how I'm a jealous, cowardly, selfish and immature little girl. That I'm a miserable person who will never make him happy. That all along she's kept her mouth shut about all my faults and shortcomings, and yet I think I have the right to criticize her.
Update 2: I've literally never criticized or even shown her any unkindness, in fact I've been far nicer to her than she's deserved. But what makes me even more upset is that although my fiancé stood up for me, I find out the very next day he's contacting her asking if she's ok. It almost felt like a... show more I've literally never criticized or even shown her any unkindness, in fact I've been far nicer to her than she's deserved. But what makes me even more upset is that although my fiancé stood up for me, I find out the very next day he's contacting her asking if she's ok. It almost felt like a betrayal and slap in my face. I just don't know what to do with all of this and if anyone could give me advice regarding how to handle this mess, I'd greatly, greatly appreciate it. Thanks!
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