So I think his schtick is that after the whole thing with that woman, he concluded that he tried to act according to his good-guy instincts and the results were just everything turned to crap, so he might as well just give up and act like society expected, self-centred and oriented to bolstering his social position. Of course, that in itself is just this bitter but naive, inverted youthful rebellion thing. He's younger than I'd realized.
This manga is really mostly about all the people they meet along the way--even the main characters' own character development mostly happens by showing what they do when they come up against other people with problems. So I don't really understand why anyone who doesn't want to meet any other characters is even reading this.