What's "going on" between the Proctors at the beginning of Act II?
In addition, we see that John and Elizabeth Proctor still love one another. That's what makes this scene so difficult, so tense. He feels guilty and angry; she feels hurt and betrayed. However, they both continue to love each other and show it in small ways, ways that we see but that they may not. For example, before Elizabeth comes into the room, John adds some seasoning to the stew on the fire. Then, when he appears to taste it for the first time, in front of her, he compliments her and tells her that it's "well seasoned." We know this is a lie—he didn't feel it was well-seasoned, which is why he added salt—but we can also see that he is attempting to compliment her, to make her feel good (though she doesn't realize that he is lying, of course—only we do). Further, when he goes to take that first bite, stage direction tells us that "She sits and watches him taste it" and "blush[es] with pleasure" at his compliment. He wants her to be happy, and she wants him to be happy as well. It is the tension between their loving feelings for one another and their feelings of pain and anger that make this scene so complex and help to explain "what's going on." They are both trying to move on and are both still struggling to do so: each one made more vulnerable by the fact that they still care for the other, each one raw from the hurt they feel.
From the most elemental of aspects, what is "going on" between the Proctors is that their marriage is enduring a challenging time. There is obvious tension between both husband and wife. The affair that John had with Abigail is taking its toll on their marriage. At the same time, Elizabeth is struggling with both her potential role in driving her husband away as well as being able to look past the affair. John, himself, is struggling with having committed such a transgression and, at the same time, no longer wanting to feel guilty for it. In both of them, the ability to let go of the past for different reasons and embrace the future is where their challenges lie.
As Act II opens, both husband and wife are immersed in this struggle. This accounts for the very off emotional dynamic existing between them. The small talk of seasonal change and harvests is concealing a cauldron of anger, hurt, and resentment in both of them. This comes out eventually in the act. It is Miller's genius to be able to depict marriage, even in the Puritans' times, in such an honest and brutal manner. There is only the long standing suffering that exists when wrong is committed. Marriage is shown as the challenge to seek to overcome that suffering. This is what transpires between both of them, or "what's going on" between them.