thats obvious from what we know bout the sensei its obv he didnt stop before the uke graduated but we cant assume that only the author knows best
I don't think he played around during that time. The author made a point at the very beginning that he was changing. And it made more obvious at the end when the sensei didn't want to ruin it by rushing or by doing anything he thought would annoy the uke. Usually in this kind of stories if there's an indiscretion is mentioned or something, but if there's not, the author makes a point to show the change. Which is what happens here
I know that the sensei trying to change himself but you know you cant help but wonder if he will change for good. Also I'm curious if sensei played during the years before the uke graduated.