Because the japanese idol fanbase is composed of extremely delusional people? And the fact that most idols are literally manufactured, and that manufactured image has absolutely nothing to do with the actress/actor (and it IS an actress or actor ) portraying said idol nowadays?
"Then all we've gotta do is make sure nobody finds out"? This is either setting this up for some blackmail style stuff or just them continuing this relationship of not loving, just fucking.
Well...I guess if it's just pure lust/sex, it wouldn't count as 'romantic contact'? Perfect logic.