Your Snape is so realistic! Things are so good in this universe, it's as if Snape really did die, and he went went to heaven. He has everything here: the potions lab of his dreams, fantastic gardens, good friends, hot sex, and someone who truly loves him. So what does he do? He fights against it with all his might, of course! The man just does not know how to be happy. His life has been devoid of happiness, except for a few short episodes during his childhood, and although the books and their author tell us that he "knew love," I think it's debatable whether anyone ever really loved him. So he can't recognize love, even when it's standing right in front of him and yelling in his face. I was so happy when he finally came around!
Your secondary characters are wonderful, too. I love your Paracelsus, Phineas, Narcissa, Lupin, Ginny, and Kreacher. "Master Harry is wasting his seed." :D Kreacher must have been happy at the end. I was too!