Personally I belive he would develope anorexia nervosa out of the stressed situation with his family. I belive Sirius would think of restricting his eating as the only way for him to have control over himself, since his parents held him in a very tight leach.
Sirius and Lupin had given Harry a set of excellent books entitled Practical Defensive Magic and its Use Against the Dark Arts, which had superb, moving color illustrations of all the counterjinxes and hexes it described. Harry flicked through the first volume eagerly; he could see it was going to be highly useful in his plans for the D.A.
this comes from my very staunch headcanon that remus broke sirius out of grimmauld place at least once
We don’t know how James and Sirius met Remus but I’ve always liked the idea that since September 1st, 1971 was super close to a full moon, Remus was super irritable and so while there all waiting to be sorted, this pureblood kid looks at him and sees that Remus has the traits of a muggle and asks “what are you, a mudblood?” And Remus, who has dealt with ignorance his whole fucking life is fed up with this kid so he whips around and just says “halfblood, pureblood, muggle born, doesn’t matter, I’ll still know more about magic than a posh wank stain like you.” And everyone is just stunned but James and Sirius are both just smiling like idiots because “oh my god we found our third.”