His jealous of the teacher,but the teacher is a good person,but the teacher played with a student,but that's normal in that world ,IM CONFUSED 
yea. Just wanna mention to other people who are new here, it is common for the Dom teacher to play lightly with the sub student to help them. Just note that in Dom-Sub verse it is a need, just like how breathing and eating is to us human, without satisfying the need, it will lead to mental and physical health issues.
playing lightly is just usually sit and praising them thats all. Just like how this manga present it as
https://mangabuddy.com/oresama-dom-wa-nade-raretai
,i clicked on the link to read it and just found funny they are from the same author of Bokutachi wa Unmei ni Kirawareteiru witch im going to re-read thanks to the response you left me there hahaha