you're not. it's just called sadism. but considering the translation conveyed the vibe he wasn't enjoying it, the fact that someone would want to push him further even though he's in pain rather than pleasure is concerning. i don't know if you read the novel and that's why, but when someone is crying out to stop and it seems they really don't want to go on anymore (some people just like feeling helpless, so they'll say stop without really wanting to stop [a kink that should be discussed beforehand to avoid confusion]), you very simply stop. no pushing further. break off the session. don't play for the rest of the day, and stay out of touch as long as your sub desires.
Well his face in the last page is so unfair. Like damn. Anyone would want to tease him moreლ(´ڡ`ლ). And just see him cry n beg. Mwahahaha.
(Fkn hell. Think I'm a psycho ╥﹏╥)