Prior to meeting Helen, Harry was relatively poor and had much more inspiration for his writing. Harry sometimes blames Helen, sometimes blames himself. He assumes that his comfortable life with Helen has made him complacent and has dulled his talent for writing. When he becomes sick with gangrene, this anger he has for Helen (justified or not) increases. On trading his old life for a new one with her, "He had traded it for security, for comfort too, there was no denying that, and for what else? He did not know." But it would clearly be wrong to blame Helen for the loss of his talent. Hemingway makes this clear.
As he is dying and immobile, Helen goes out shooting. Combine this with the fact that he lived with the comfort of her money, and it is possible that Harry felt emasculated by Helen; but it is his choice to stay with her in this comfortable life. He can blame her, but it is his choice.
Hemingway portrays Helen as a genuinely caring person and she becomes more of a mother figure than a lover to Harry, especially when he becomes ill. Harry paints her as a "rich bitch" but one who genuinely cares for him. And Harry seems to envision himself, his life before Helen, as masculine, strong, exciting, and adventurous. However, in the context of the story (in Africa), Harry is weak, cynical, and even cowardly. Helen, on the other hand, remains positive and strong. That may be a bit harsh considering Harry is facing death, but his weakness shows.
In this analysis, Helen is the strong one in terms of character. There is also a bit of reversal in terms gender roles. While Harry is basically an invalid, waiting at the tent, Helen goes off hunting. She takes on the typical male role while also becoming like a mother to Harry. Harry crumbles when his traditional male role is gone. Essentially, Helen becomes the dominant one in the relationship.