(Up to chapter 7)
When we first met Jody I thought that he genuinely cared for Janie (naive maybe, but in the context of Janie's stale marriage with Logan I was hoping for a breath of fresh air). It was impossible to know who Jody was until they got to Eatonville, and by then it was too late.
Jody didn't talk to Janie in the woods for three days because he loved her. He saw in Janie a possibility to advance himself. He saw a beautiful, proper lady... just what he pictured he would need as mayor of Eatonville (the mayor needs a stately wife). When the couple gets to Eatonville we see that he cares a lot about her image - she needs to be seen at the right places, she needs to play hostess correctly, she needs to say the right things (refrain from speaking in many cases), etc. Janie falls from a marriage that--while stale and uninteresting--was safe/stable to a marriage in which she is a prop to advance Jody's position in the community.
Janie is a part of Jody's quest for power. He is not cruel to Janie for no reason--it is just his view of the world and his quest for power that brings forth frustrated anger.
However we have begun to see the beginnings of rebellion in Janie (such as her speech at the end of chapter 6 and all the hints the narrator gives us that she was sad/tired of the marriage).
We know that Janie ends up with some guy named Tea Cake (from the prologue). It's only a matter of time until something blows, and the more egocentric that Jody becomes, the more tension is built.