This is such an imporrtant development for Yoonseol and that's why this scene is so critical; he is a highly sexual person (yess boo with a libido) and, although it might not be such a major deal to the average person, sexual compatibility is a big factor he has to consider when getting into a relationship - so to see them both enjoying the moment is so ε=ε=(ノ≧∇≦)ノ I am so happy for these two and ready for what's to come
I have re-read this one so many times and I am still waiting for them to use each others first names DX