Oh God he is a cringe purity worshiping loser.
Kinda yes and not.
Mc is a purityfag, but he has a point here.
As MC expressed in his thoughts, he was aware that this woman was likely sexually experimented, considering her more mature sociable flirty personality. He had no confirmation until this chapter, but it was rather obvious.
But the things she said in this chapter... It made her intentions towards him -a virgin- sound like "let me take your virginity so I can dump you and jump to the next virgin guy in the line". And then she followed by commenting about how first times were important and left a mark on people, which made MC realize she could "mark him" but he wouldn't be able to do the same with her, because she already had her first time with someone else.
So, MC, who seemed to wish for a serious relationship, just deflated at the reality that he is possibly just a night stand for his woman. No one really special, just another guy she wants to have sex with.
EDIT: ...Of course, its uncertain if she really mean all that shit, or as the series said, she is maybe just playing with him. Maybe she wants him to man up, because I feel like she wouldn't have kissed him at the morning if she didn't care about him.