What is Patrick and Mary's marriage like?

"Lamb to the Slaughter" can be read as a portrayal of the love-hate relationship that exists in many marriages. George Meredith wrote about this painful kind of relationship in his long series of sonnets titled Modern Love. The first lines of the first sonnet in the series show the tension that exists in the marriage Meredith is chronicling (undoubtedly his own).
By this he knew she wept with waking eyes:
That, at his hand's light quiver by her head,
The strange low sobs that shook their common bed
Were called into her with a sharp surprise,
And strangely mute, like little gasping snakes,
Dreadfully venomous to him.
In "Lamb to the Slaughter" Patrick Maloney is withdrawing from his wife. He no longer wants to be with her. The more he withdraws, the more attention she gives him. Is it really love on her part, or just dependence? The more attentive she becomes, the more her husband withdraws. The marriage is dying. It would have died "of natural causes," so to speak, if she hadn't ended it so finally and dramatically with a frozen leg of lamb. She seems to become a "liberated woman" with that fatal blow. It is as if a different person concealed inside her is released from captivity and servitude.