This is quite lovely. Snape's posture is indicative of distress and exhaustion and uncertainty. His hair, too, is pretty much perfect. As to his face, perhaps his nose needs to be a bit more distinct? It runs in an almost straight line from his forehead instead of descending then hooking outward. And his eye slants upward perhaps a bit more than it should. Even so, his expression conveys the emotion quite clearly, fatigue and troubled thought. And I quite like the texture of his shirt. Also, yes, the cat!Patronus is very well drawn.

Nicely done. You catch something about Snape that rings true. But then, I love scowly!Snape.