Abigail was a servant in the Proctor household, although she was fired by Elizabeth Proctor who suspected Abigail was having an affair with her husband.

John: Abby, I may think of you softly from time to time, but I will cut off my hand before I reach for you again. We never touched.

In the final act, Elizabeth says to John, ""I have sins of my own to count. It needs a cold wife to prompt lechery"… "I never knew how I should say my love. It were a cold house I kept." Along with the fact that she had been "a long time sick", this is the cause of John's affair with Abigail. Elizabeth blames herself for Johns affair with Abigail.

Affair
is in
the Air

Abigail: Aye, but we did!