Johanna truly wishes she could love Anthony like she pretends to.
She wants every "I love you" she murmurs, every kiss she gives him, to be real, but they never are. It's all a lie, all part of her plan to escape the Judge.
Anthony's the first person so willing to help Johanna, and she takes advantage of that. She drops a key from her window, sneaks him into the house, agrees to marry him, all without knowing his name, just to get away from here. He's so in love with her that he'll do anything for her, and at first Johanna thought she would feel the same about him. But she doesn't. She tries to look into his eyes the same way he looks into hers, tries to imagine a future where they're married, but she can't. They are not meant to be together, no matter what Anthony believes.
For Johanna, all of this is acting, pretending, lying.
And it'll stay that way until she finds the courage to tell Anthony the truth: that she's never loved him.