ENOUGH with the chocolate already.
He is NOT obsessed with chocolate. He doesn't eat a single piece, for example in Order of the Phoenix.
Chocolate is the Wizarding remedy for an encounter with a Dementor. Remember how pleased Madam (note, please, *Madam*, not *Madame*. Poppy is not French) Pomfrey was when she learned that Lupin gave the students chocolate? "Thank goodness someone knows his remedies."
The other times he gave Harry chocolate was after Patronus training, which meant he had to encounter a Dementor!Boggart, and apparently that has much the same effect as a real Dementor, which doesn't make any sense, but whatever.. Not only that, but he never eats it himself after those lessons (does he even eat any on the train?)
I know it's cute; I know it's become a fanon character trait and I know it seems to make sense, but it's NOT canon.