Very nice and well written piece. Patroclus seemed dead right to me, since in canon he's a strong warrior with a rather soft heart (or far more than the era's norm, anyway). I never liked the Achilles-being-invulnerable version for I prefer him in the Homeric/Epic Cycle-verse in general, but you made it work by having Patroclus feeling at ease with befriending Achilles for not being able hurt him like he did with his old fellow.