Take a story's temperature by studying its tone. Is it hopeful? Cynical? Snarky? Playful?
Sutter Keely, our narrator and main character, is as oblivious as they come. He's only focused on his own thoughts and feelings and desires, and so he either completely misses or grossly misunderstands other people's words and actions.
Like, the reason Cassidy breaks up with him comes down to the fact that he wasn't listening when she gave him an ultimatum. We see it directly from Sutter's perspective and everything: "Here we go. Lecture time. And I'm sure what she's saying is right. […] I just can't keep my mind focused on it when she's sitting there right next to me looking like she does" (3.33). Truth: doesn't this sound a little like your internal monologue when your dad is lecturing you about taking responsibility for your actions.
He doesn't want her to be mad at him—that affects his world and Sutter's #1 priority is making sure nothing changes, ever—so he'll pretend to pay attention just enough to calm her down. Still, her feelings about their relationship don't penetrate into his universe in any real way—meaning that underneath that nodding exterior, he's totally zoned out.
But Sutter isn't just oblivious to the things that might hurt him. He's also oblivious to the things that might actually help him—like Aimee's love and concern. Even after everything Aimee has said and done, he still can't believe she really loves him: "Of course, I'd believe someone loved me," he says. "It just seems like that's pretty impossible to know for sure" (65.2).
Sutter is so oblivious that he really thinks Aimee will be happier without him. He's trapped inside his own head, completely wrapped up in the version of reality that he's created.