I don't think your mother wants the best for you. She wants the best for her. She somehow derives enjoyment from exerting control over you, maybe because so much has happened to her that is outside of her control? Who knows.

My mother once told me that a guy who had dumped me rather cruelly two years earlier was the only boyfriend of mine that she ever liked, like I should go back to him.

The situation you have with your mother really reminds me of my situation. When my parents got divorced, my father financially abandoned us. My mother worked three jobs and sacrificed a lot to take care of us. It was nice of her to do that. For years I admired her for it and scorned my father for abandoning us.

However, that 'niceness' does not make up for the controlling/martyrdom/etc. I was the oldest female. My mother used me like a friend because she did not have many of her own and really made it hard for me as an adult to have normal relationships with other people. I still struggle with it.

So I think you are on the right track to be questioning your mother's judgment, witholding info, and trying to live your own life on your own terms. It does get easier with practice to distinguish between appropriate maternal behavior and inappropriate nosiness.