A stage direction on page 54 says that elizabeth 'has suddenly lost all faith' in John.How the dialogue made her to do this?

Elizabeth sees John's moment alone with Abigail as another betrayal to their marriage vows.

"Proctor, stubbornly: For a moment alone, aye.

Elizabeth: Why, then, it is not as you told me.

Proctor, his anger rising: For a moment, I say. The others come in soon after.

Elizabeth, quietly - she has suddenly lost all faith in him: Do as you wish, then. She starts to turn."