These are my thoughts on the title story only.
Susan Rawlings is married to a man she has loved, has four beloved children, is financially comfortable, and seeks a centre and purpose for her life. (view spoiler)
Lessing's protagonist has a terrible hunger and the root of it is the emptiness of her inner life in the situation of a financially secure, initially happily married housewife. Little colour is given to Matthew's portrait; is it unimportant to Lessing's purpose. He is typical. The briefly sketched character of Sophie Traub, the agreeable German au pair who seems to understand Susan's plight, in so far as she can imagine a healthy response to it, is more significant and interesting. Sophie seems to be a healthy mirror for Susan, even a younger self, representing possibilities and freedoms no longer open to Susan.
Lessing does not need to describe the freedom Susan is starving for; her desperation is absolutely clear and her husband's rational objection based on the comparison with his own life is met with the reader's sympathetic frustration. Matthew can carry on a secret affair; he has an independent emotional life. The constraints on his time reflect his power and control and are utterly different from the ostensibly light demands on Susan, which render her purposeless and subject her emotions to scrutiny from all sides. Though we understand her thirst, her extreme solution highlights the severity of her disease. She is ill and therefore society is ill. Susan's life is her culture's ideal for a woman, yet it drives her to despair. She is so damaged that the 'creative darkness' she accesses does not heal her.
All artists have some kind of creative inner refuge, which satisfies and is restorative, even transformative when it is productive. Susan lacks a creative outlet (she has worked as a commercial artist so she has the mechanical ability to express herself) because she lacks stimulation - this is what patriarchy has deprived her of, no? When Lily paints a tree (in a creative space that enlarges her spirit) it is a tree that Susan could never see in the garden that threatens her and where she senses the presence of her 'enemy', who takes a man's image. She is oppressed and her emotional space is pressurised by this monster, who is a creation of her guilt and resentment, of the 'aridity' she can't fathom. Perhaps it's her response which is pathological - we want her to confront this demon and instead she retreats and retreats - but the whole story is pervaded by a sense of inevitability, as if no escape from him is possible. So the creative confrontation, the artist's episode of self-discovery, is not accessible to Susan, and Lessing sees this as a fatal disaster.