What should we do?

Although having finally reached chapter 30 (yay!), I find myself still asking many questions about Jim. In fact, I'm not even sure if I got some of the facts right, its all very messy. But to get to the point, I think Jim is quite fickle because it is as if he cant decide what to do all the time, and sometimes I find myself getting really irritated by him. So in an attempt to understand his character, I tried to imagine myself in his dilemma, and I realized that if I had chosen to play romantic hero and tried to save the people instead of jumping off, it would only be because I fervently and totally believed that it was morally and socially right to fulfill my duty as officer. Yet the modernist narrative techniques in this text and many others suggest that there is no way of ever fully understanding Jim, and by extension no way of ever knowing the truth or what-is-right.

But if there are no universal truths how can we believe? And if we can't believe, how can we act 'appropriately' on this belief? In other words, since there is no universal truths or values, what justifies anyone's actions (e.g even the seemingly correct French officer's act of fulfilling his role by staying aboard the Patna and seeing it through the storm)? How can we resolve this conflict? Is this one of the issues that the novel is rising as well? I'm not sure.