In The Beast in the Jungle, by Henry James, May Bartram keeps her silence until the very end of her life, thereby dooming not only Marcher's hopes for happiness but her own as well. Why does she do this? Is this plausible?

May Bartram understands Marcher better than anyone else does. She must bear the burden of taking care of herself as best she can during her illness. May is honest in warning Marcher about pain, suffering, and loss. He is incapable of understanding what she says because he is not grounded. May is drawn to his ethereal qualities in part because they balance her temperamentally, but she knows that he is deaf to her words. The man lives in a fog. He refuses to be responsible for his own happiness.
Part of Marcher's loss stems from his obtuseness. She tries to warn him that he is losing out, but he just doesn't get it. This situation is far more than plausible; it is realistic. Were May to try to use her love as a rope to bind him to her, Marcher would just panic and run away. What she understands is that he has to have these epiphanies in his own time. She just ran out of time to wait for him to grow up.