We got the impression in Act One that John Proctor and Abigail had an affair. It becomes clear, at least to Elizabeth, that although Abigail and the other girls initially made accusations of others in order to avoid getting into trouble, it seems that Abigail might see this as an opportunity to accuse Elizabeth and then have John to herself. In Act Two, Elizabeth tries to convince John to talk to Abigail and make things right before it is too late. She says, "You have a faulty understanding of young girls. There is a promise made in any bed-" Then she says, "Spoken or silent, a promise is surely made. And she may dote on it now---I am sure she does---and thinks to kill me, then to take my place."
Shortly after this conversation, Reverend Hale shows up and tells them that Elizabeth's name has been mentioned in court.
Also, in court, Abigail clutches her stomach in pain and blames Elizabeth for it, knowing that Mary had planted the doll in Elizabeth's home with a needle in it, indicating witchcraft. When John Proctor tries to convince Mary to tell the court about the planted doll, Mary tells him that Abigail will charge him with lechery (adultery).