I'm guessing that he plans to be the one Woojoo runs to when he finds out the truth. He can always say he didn't know what the Honey Trouble was when he gave it to him and was just told it was 'vitamins' too. I think he's biding his time since he can't get in between them right now
Why did prof. Cha leaved the wooju to juyeon. İ did not understand that part