Lestrade is all: "This is a drugs bust... if it’s not drugs or evidence I don’t f***ing care. Eyeballs aren't my division, neither are microwaves. Coffee is my division. Doughnuts are my division. Mmmm, Sherlock’s delicious f***ng arse is my division. Who would've guessed..."
At first he hid the drug addiction from John then it came out all so suddenly. He saw how John fussed over him at times and he wanted to put up a strong front. I think this wasn't only a confession to John, this was an admittance to himself.