In Act 4, Scene 2, Lady Macduff asks Ross why Macduff has left. She feels that he has abandoned her. Ross is vague and simply tells her to be patient. Ross says he must have had a good reason to leave. Lady Macduff is not convinced. She thinks he left because of fear. She is so hurt that she says he does not love his family and he is a coward:
He loves us not;
He wants the natural touch: for the poor wren,
The most diminutive birds will fight. (IV.ii.11-13)
When she says "He wants the natural touch," she means that he lacks (doesn't have it, so he "wants") the protective ("natural") instinct. Even the smallest bird will stay and defend its family. But, in Lady Macduff's mind, Macduff has run away.
Regarding his choice to leave, she says, "All is the fear and nothing is the love." She even tells their son that Macduff is dead. When the son asks what she will do without a husband, she says she can buy twenty husbands at the market. She answers her son that Macduff is a traitor. "Everyone that does so is a traitor and must be hanged." Lady Macduff is so upset that she even tells her son that Macduff deserves to be executed. She will not consider that Macduff has gone to England for a legitimate reason. In fact, he has gone talk with Malcolm about restoring order in Scotland.