Tristana was another one of Buñuel’s films that follows a girl who struggles to find her balance when the weight of her new life comes crashing down on her innocence.
I think her struggle to accept the authority of Don Lope who—at most, was a bitter old creep that took advantage of her—made her spiral into this bitter woman herself. She was in a vulnerable when she met Lope and he took her innocence and try to cover it up as protection from other evils out there in the world. When in fact he was the biggest evil in her life. When it came to how she controlled herself; rebelling against him, going with another man, etc—all roads lead back to the way he shaped her ethics. She did not want to get married to the man she met, she didn’t believe in marriage and thought of this relationship as just a temporary thing that would last until the joy ran out. Not a thing to cherish and work towards but something that brings temporary happiness with another person.
On top of that we did talk how she took herself back by being controlling and bitter to Don Lope. However I believe that it was her being a product of the world around her—the hardships she had to go through and the people she had to face.