What happens to heejae at that club?

They probably drugged him and harrased him a bit but then that woman stopped them and called the secretary before they went too far, at least that was how it looked like to me bc the brother had already said once that heejae should use his body since he was stupid.

So the red stains on his shirt were blood or lipstick?

I don't really know but I guess it can be that, in the end I can't think of anything else that could have happened