There are two aspects of the initial stage directions that we are given at the beginning of this act that indicate that all is not well in the marriage of the Proctors. Firstly, when John enters his home, notice the way in which he "halts for an instant" as he hears his wife singing. The sudden effect of her voice on him and the way that he stops what he is doing suggests that there is something wrong. Secondly, John's testing of the food that he is going to eat and the way that he is "not quite pleased" with it, adding salt himself to give it more flavour also perhaps indicates that there is something wrong, especially in the way that he then goes on to lie about it to Elizabeth, saying "It's well seasoned."
The last major clue that we have comes after the dialogue has started. After John tells Elizabeth that he means "to please" her, we are told that she finds it difficult to respond. Then, notice the following stage directions:
He gets up, goes to her, kisses her. She receives it. With a certain disappointment, he returns to the table.
The way in which Elizabeth only "receives" her husband's kiss instead of responding more emotionally and physically, and John's subsequent sense of disappointment clearly conveys the way in which there is something wrong in their marriage. We have seen John lie to please her and then Elizabeth's cold response to his physical advances. We are definitely presented with a marriage that is experiencing some problems.