My (F25) GMIL (F69) is two faced and I can’t leave.

Please help, I need to figure out a way to deal/cope with my current situation in a mature way.

So, my fiancée and I have been living with his grandmother for the past 6 months. We live in an extremely high cost of living area, and had to move in with her temporarily while we save for a place of our own (we do pay her rent).

I thought I was getting along with her and making inroads. My partner told me he wanted me to try and be close with his family, so that’s what I did. I even opened up to his grandmother about how my mother had to raise me mostly by herself, and try to keep me safe from my alcoholic father. My fiancées grandmother listened to me, shared some of her own stories, and has been very polite. To my face.

So I was very surprised when my fiancée told me that his grandmother had told him to “watch out” for me. She told him that I “seemed like the kind of person who would use your kids against you, or try to keep them away from you”. My fiancée of course stood up for me to her, and said I was not that kind of person. When he told me what she said, I was crushed. I opened up to this woman who has taken me into her home, and she makes this kind of cruel judgement on me?

I have only ever behaved politely and warmly to her. I have never given her any indication that that is my character. I feel extremely hurt that I am living with someone who views me in this way. Unfortunately, we can’t afford to move out for another month and a half. I need advice on how to move forward, if I should confront her, and generally how to cope with living with someone who behaves nicely to your face but then says vile things behind your back.

TLDR: how to deal with a GMIL who acts polite in front of you but trash talks you behind your back.