The Proctors' marriage is dynamic, to be sure. It suffers from some common elements in many relationships--insecurities, guilt, temptation, and distrust--but is held together by love.
Elizabeth is insecure; she admits late in the story she didn't feel worthy to be loved by John. Yet, when she suspects the relationship between John and Abigail, she loves him enough to fight for him and sends Abigail away.
Guilt is primarily John's cross to bear, as he has transgressed against not only his marriage vows but also his personal moral code and his spiritual beliefs. His actions and reactions from the time we meet him are nearly all based on the premise of guilt, though he is finally able to confess openly out of love for his wife.
John's temptation is Abigail--someone Arthur Miller says has "an endless capacity for dissembling" (lying). She is used to getting what she wants through manipulation and force, and John was an easy and attractive target for many reasons. It is John's sin that he fell for such a temptation.
The most common dynamic between them throughout the course of the play is distrust--and rightly so. A broken covenant is no easy thing to forgive, especially in the context of their Puritan beliefs; yet they are struggling for some normalcy and a return to the love. The most pointed picture of this struggle is John's recounting of the Ten Commandments; he and Elizabeth eventually come up with all of them, but the undercurrent of guilt and shame and awkward love is the subtext for this exchange.
The first time we see them together is awkward and uneasy; however, by the end we understand that they do love one another and the rest was only a painful interlude in their marriage. This is the dynamic nature of their relationship as well as most long-term commitments. Things happen, but the love survives.
I think that Miller shows the relationship between the Proctors as dynamic to reflect what a good relationship should be. Unlike most of the associations in Salem that are static, at best, Miller shows the Proctors' connection as going through change and a sense of vibrance even at its very worst. At the start of the play, there is some level of tension present. It might not be tension as much as it is a sense of being unsettled about the nature of their relationshp. Once the accusations start, the natural tendency is for each of them to seek to take a route of least resistance. Elizabeth wants John to sign the confession and for his part, John struggles with what to do. Miller's depiction in this relam shows that the relationship is changing. It is no longer guarded and isolating. Rather, it is collaborative and one fraught with complexities and challenges. When Elizabeth lies for her husband on the stand, it shows a level of commitment between both of them, where the notion of sacrifice is a far cry from what was shown at the start. Here again, in the midst of the worst of what humans can do, there is a sense of redemption in their relationship, in this bond. It is only through Miller's genius of showing this dynamic sense of consciousness where we are able to see this. We see this when John is imprisoned and Elizabeth pleads with him to confess, and, of course, when John refuses to confess and Elizabeth understand why her husband must do what he feels he has to do. It is at this point where we fully see how wonderfully strong their relationship is, one that will survive false accusations and even death. It is thie sense of dynamic richness that allows us to fully embrace the fact that there might be some level of hope and redemption in a situation devoid of it.