Death
As is universally understood regarding poetry, the poems revolve around death. Death is inescapable for Hughes. It's what inspires him to leave his wife and kids, because he is so concerned that he's cheating himself out of the life he has left to life by staying with someone he hates. Trapped in this relationship which he despises, he becomes aware that he's only fulfilling a role for his wife. After he father's funeral she admits to Hughes that she likes him because he is so completely like her dad was. She married him because she wanted him to replace her father in her life. In death, the truth comes out that she never loved him for who he was. On the other hand, he imagines what his life would be like without her and concludes that he could never live with himself if she died, but he will live apart from her for his own sake. His final poems address his despair following her suicide.
Sexual Frustration
Hughes and his wife have an unhappy marriage. She is unwilling to deliver what he needs to be sexually satisfied, and he honestly does not care about her needs. When he leaves, he states that it's because he deserves to be with someone who will treat him the way he believes he deserves to be treated. He wants his own space. He doesn't want to feel obligated to someone he's no longer attracted to. This selfishness leads her to believe she's unattractive, and her consequent self-doubt further complicates their sex life.
Jealousy
Plath knows that Hughes is unfaithful to her. Despite her best efforts to keep him interested, he engages in constant affairs. Eventually he moves to California, leaving her and the kids behind. She allows it, but she doesn't really get a choice in the matter. When she visits him in his new apartment, she visibly cannot control her jealous intentions as she scours the place for signs of the latest woman he's been engaged with. Her hateful attitude stems in part from his complete abnegation of his role in their family after he left.
Guilt
Hughes loves his children. They are a constant presence in his life. After his wife commits suicide, though, he learns the unspeakable pain of true remorse. Seeing her face perfectly mirrored in the faces of his little ones nearly drives him insane. He is wracked with guilt for how he handled his marriage and the consequent irreversible pain he caused for his children. While she is gone, he is left behind to keep trying to pick up the pieces of the mess they made together.
