Alex had been confused by Cody's line of questioning at first—and the fact that he thought he needed to show up at his work to get any time with him—but after talking to him he was fairly certain he understood. He was feeling left out because he wasn't grasping a concept as quickly as the rest. As someone who loved learning more than any of the others except Carmen, that would definitely bother him.
It wasn't his fault. Everyone figured things out at their own pace.
Love was an especially difficult concept because of the way they grew up. If he didn't have a person he cared about deeply, it made sense that he wouldn't be able to understand love. That wasn't his fault either.
Alex wished he could find the right thing to make him feel better but wasn't sure what would work. He and Cody didn't actually spend all that much time together.