Well, you have your opinion and I have mine, I just wanted to give you my point of view on this scene, so let's go. Chapter 5 is reserved only for showing Emma's mother's past, and the connection between Emma and the MC, even before this scene happens there's a whole scene of the two characters crying, as soon as they discover the whole truth, it's not as if the moment the truth is revealed to the MC, Emma just jumps on him and they start having sex as you make it sound. When the sex scene between Emma and the MC happens, it's a cathartic moment, it was meant to be, because it's the moment when the two characters can be themselves, do what they haven't been able to do in those years apart. They're not just naked, they're completely naked of any fear, of anything that might hide who they are, they're just the two of them, and it's at that moment that they hug, cry, kiss, etc. The sex scene serves precisely to show all the feelings the two characters are carrying.