I know a lot of people think AR kissed DO but I personally think that they didn't kiss. They only showed the back…
My thoughts are that maybe he hugged her or something as it seems unlikely he’d kiss her given her status as his student at the time it would’ve been inappropriate (and because of AJ of course).
This is what he thought in the beginning but I think the events in this episode made him understand he was wrong…
Also she definitely didn’t need to say to him she has him so that he could look after Sang Tae, that felt horrible for me, like you just really shouldn’t say or do that ever.