Godfrey Cass was actually a good man with very poor initiative, and a penchant to detour from what the main purposes in life should be.
When he was considering confessing the situation about his crazy marriage to Molly and his eventual ruin and lack of money (not to mention giving his brother Dunsey his horse to sell), he was really measuring what would be the worse consequence: Would it be worth telling his father and facing the rage and after actions that his father is most famous for? Would it be easier to just go with the flow and wish for the best? If he was disinherited, he would have to suffer the shame of living under the shadow of who he once was or (even worse) enlist in the military to earn at least half of his reputation.
It was as if he was living for the moment in the process of determining whether to tell or not. He would cherish the opportunity of seeing Nancy and just wait and see what cames up. He was quite nervous but understood that all of this had been his own wrongdoing.