I would actually argue that, of the two of them, Harry does show potential to grow, as is evidenced by his final decision to walk away. Severus's stagnation, on the other hand, is probably the most IC thing in the story. He's stuck in the past and doesn't understand that, even if he lets it go, he will still have something left in Harry. But his attachment to Harry is largely based on his past. It's a catch-22 for him. In Harry's view leaving, while it is probably the worst thing he can do to Severus, it's also the best thing he can do for Severus, and for himself as well.
But you're correct in that that's only the dimmest of insights on Harry's part--more instinctual than anything else. Maybe he's too hung up on his own sense of betrayal; he has the potential to grow past it, though. They were happy at some point though (in my mind at least). In my mind's eye, years after the end of this story, I imagine that Harry will look back on his relationship with Severus when he gets old with wistful regret and affection. If nothing else, Harry has always shown the capacity to forgive--something that Severus lacks, especially when it comes to forgiving himself.
Thank you for your review and I'm glad you liked the story.