It's not that he enjoys studying. He's just working hard towards his goal. The enjoyment he has is generally when he has good results... which seems to be a rarity so I'm not sure his goal is really attainable, with or without Megumi's distractions. Like that time he dropped from 5th in his class to around 10th on the exams, that might seem like a large change but in reality some of the top people in his class were in the 100-300 range nationwide, while he was somewhere around 4000. It sort of seems like he's not doing well enough that her distractions are even causing any serious damage in the grand scheme of things.