In The Crucible, why is the scene between Elizabeth and John Proctor important, and what does it reveal about their relationship?

In the first scene of Act 2 in The Crucible, Miller introduces Elizabeth Proctor and provides the audience with an intimate glimpse into her marriage to John.  By this point in the play, the conversation between John Proctor and Abigail Williams has already taken place; so the audience knows that John was unfaithful to Elizabeth.

As the scene opens, Elizabeth has been waiting for John and instead of greeting him affectionately, she immediately questions why he is "so late."  This sets the tone for the rest of the scene: Elizabeth questions John's actions, motives, and words, and John resents her suspicion and emotional distance.  While John's and Elizabeth's words are quite telling in regards to the tension between them, Miller's stage directions are even more significant.  When John kisses Elizabeth,

"she receives it. With a certain disappointment, he returns to the table."

John had made the effort to get up, go to his wife, and demonstrate affection, but it is still to difficult for her to return her trust and sincere affection to her husband.