(Sorry I keep replying to things! I have too much time today and I'm so excited about Prep.)

Oooooooh, "The Phoenix" looks like an excellent story from which to make a novel! You already have two complex, interesting characters and a compelling relationship to start with. Your protagonist, with the walls he's built to protect himself (replete with spikes!), is already rife with opportunities for internal and external conflict that could affect the way he forms relationships.

I made a novel from a short story once, and it's totally doable! I hope this one works for you!