Why does my mother have to lie?

My mother is in the process of divorcing her second husband because he cheated on her with a younger woman and lied many times about it. I helped her through her grief and she even got me to give her copies of the emails her husband sent me to include them in the divorce proceedings which means now I am not in good terms with him. I've been trying to call her for a few weeks and since I couldn't reach her I called my brother who lives close by her and he told me she is in Mexico with a group of friends. I know this is not true because she doesn't have any friends and while talking to my brother I could tell he was lying. Now it turns out a friend of mine saw her at the airport with the husband but my mother didn't see her. Why is mi mother hiding the fact that she got back together with her husband from me and instructing my brother to lie to me about it? She has always had a tendency to lie but this seems like too much. I am also upset because before this she was calling me on the phone every single day and then all the sudden she takes off with this guy and she has no use for me anymore. I feel stupid and used. Thanks for reading.