Just to hammer it all out and down:
Olivia: had sexual relations with Peacock before her marriage, and had relations with Macafee after her marriage. She is unhappy, and the source might be as mundane as finding herself no longer in the courtship limelight
-- feeling unfit to be a wife
Smart: married to Olivia, unsettled by her activities with Peacock and Macafee.
Macafee: happy.
Peacock: Smart's old friend, Olivia's spurned lover, he is presumably murderously jealous of Olivia's trysts with Macafee. Maybe he would rather kill Olivia than Macafee because he doesn't think Olivia would visit him if Macafee were eliminated; or maybe it is cloaked in Peacock's mind as outrage for his friend Smart that Smart's wife is cheating on him.
=mantis=
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