One reason Elizabeth is suspicious is because John Proctor had told her he last saw Abigail "with a crowd". He then admits that when Abigail told him that what had happened in the woods "had naught to do with witchcraft", he had been with her "in a room alone". Although he argues that they were only alone "for a moment...the others come in soon after", Elizabeth feels that he has not been "open", or honest, with her.
When Elizabeth tells John he must go to Salem and reveal to the court what Abigail confided to him, John replies that he "will think on it...wondering how (he) may prove what she told (him)". Elizabeth sees it differently, asking him, "if it were not Abigail that (he) must go to hurt, would (he) falter now?" She believes he hesitates because deep down inside, he still has feelings for Abigail and doesn't want to hurt her.
Abigail then accuses Elizabeth of witchcraft, and Elizabeth concludes that Abigail wants her out of the way so she can "take (her) place". She tells John that he has given Abigail "hope" that he still cares for her, because when John passes her in church he "will blush". When John says he blushes only for his shame, Elizabeth tells him "then go and tell her she's a whore". He agrees to do so, but angrily, which Elizabeth interprets to mean he is unwilling (Act 2)