MC has good self control, and I like that they show that a man is always a man, ie him getting hard by seeing her. But even if a guy turns out a hot girl in that situation, it's not because he isn't interested - he definitely is. A man is always going to be interested in that kind of situation. And being interested is how someone catches feelings, so even if he doesn't like her now, he would eventually, unless he finds someone else quickly.
Sayu should strike while his iron is hot, a man can only turn down so much