tbh I can understand why some people feel the story is weird. Five years is indeed a long time. Maybe it makes sense if both of them came from a rural area or some part of Japan where virginity still considered a high value, but clearly, that is not the reason here, since MC reason is just that he is not in the mood and both of them can talk about sex without blushing and said, "W-what are you talking about?". But yeah, this is rom-com, I don't think it's good to think too hard about it.