Oh my, this was so funny and sweet and funny and poignant (and did I mention funny?)! The turns of phrase so often caught me with my mouth full, that I just gave up eating. (You're great for my diet)
Your characterization was superb! I adored your Harry: sweet, loyal, still learning about himself and his friends. It is wonderful that he was taking time to figure out what he wanted. Severus was just more of himself--delicious. I this line melted me: Snape looked at him for a long moment. "It was therapeutic, at that. For the first time in memory, I was able to fully express my displeasure, holding nothing back," Snape said dreamily.
The development of their relationship was almost inevitable because of the nature of their characters. You wrote it beautifully!