Abigail Williams and John Proctor are former lovers who engaged in an affair seven months before the start of the play. Abigail is John's former servant; she was dismissed from her duties after Elizabeth, John's wife, discovered their affair. According to Abigail, it was a passionate, exciting affair, and she desires to continue seeing John. In act 1, John Proctor visits Reverend Parris's home to inquire about Betty's strange illness and briefly interacts with Abigail. Abigail expresses her strong feelings for John, who insists that she forget about their prior affair and move on with her life. Although John may still harbor feelings for Abigail, he is adamant about remaining faithful to Elizabeth and regrets committing adultery.

As the play progresses, Abigail begins falsely accusing innocent citizens of witchcraft and attempts to get rid of Elizabeth in order to have John to herself. Abigail then stabs herself in the stomach and claims that Elizabeth sent her spirit out to kill her. When court officials visit Proctor's home in act 2, they end up arresting Elizabeth for attempted murder. In act 3, John Proctor attempts to undermine the corrupt court and expose Abigail as a liar by confessing to infidelity. John Proctor's confession astonishes the court but ruins his reputation. Tragically, John's confession is not strong enough to disband the corrupt court, and he eventually dies a martyr.

Abigail and John Proctor are former lovers in The Crucible. They became lovers when she worked in his house and broke up when he decided to reconcile with his wife, Elizabeth.

Abigail is the niece of the Puritan minister Reverend Parris. When he finds them dancing in the forest, they claim they were affected by witchcraft to avoid punishment. This leads to the beginning of the Salem witch trials.

Abigail accuses John's wife, Elizabeth, of being a witch; Elizabeth protests. It's clear that the accusation stems from Elizabeth firing Abigail when she discovered the affair between John and Abigail. In the seven months since she was dismissed, Abigail hasn't been able to find a job in any other house.

Abigail hasn't moved on from John, but he is determined not to go back to her. He doesn't want to cheat on his wife. He only wants to strengthen his marriage and earn forgiveness. He's determined to expose Abigail as a fraud so that they can stop innocent people from being tried and convicted.

John chooses to stand up to Abigail, the Reverend, and the town. He says that Abigail is only doing what she's doing because of their affair. She refuses to admit it and John is accused of witchcraft, just like his wife. Ultimately, he is hanged for his perceived crimes.

As the play begins, the audience understands that John and Elizabeth Proctor, a couple in their thirties, had employed Abigail Williams, a seventeen-year-old girl, as household help while Elizabeth recuperated from a difficult birth.  Abigail and John have engaged in an affair, and Elizabeth has found out about it and dismissed Abigail, and (according to Abigail) quietly put out the word in Salem that she should not be hired by other families-- without detailing what happened.

Abigail has mistaken John's sexual interest in her for genuine love. She is desperate to win him back; she believes that if Elizabeth were out of the way, she would become John's second wife.  This is the reason she was conjuring a spell in the woods with Tituba and girls from the village.

John is committed to restoring his relationship with Elizabeth, and though he is unsettled by Abigail's attraction, vows that it is over between them.

The short answer to your question is that Abigail Williams and John Proctor are ex-lovers. We discover in the first act of The Crucible by Arthur Miller that the two of them had an affair. Abigail was the Proctor's servant girl, and it was, at least according to her, a very intense affair. 

We learn that the affair ended seven months ago; however, Abigail makes it clear that she wants Proctor back. Proctor, on the other hand, is determined not to resume their relationship (which is just a bit different than saying he does not still want to be with her). Proctor says it this way:

Abby, I may think of you softly from time to time. But I will cut off my hand before I’ll ever reach for you again. Wipe it out of mind. We never touched, Abby.

John Proctor wins this battle of wills and he does not resume his relationship with Abigail Williams. Nevertheless, this relationship is the crux of all that goes wrong in Salem during this witchcraft frenzy. It seems to me that you have not read very far in the play yet, so I won't spoil anything for you; however, I would encourage you to keep this relationship in mind as you read. Abigail is a liar (Miller says she has "and endless capacity for dissembling") and she is desperate to get her lover back. It is a deadly combination.