Based on lyrics.. he (ysh) went out w the blue girl (perhaps his gf) for a date. But during the date, he show awkward smile and conversation because he just don't love her. Suddenly he is more attracted to watch other people (the black dress girl w his bf) and she feel upset about that but still she love him (ysh). Then he (ysh) went from the toilet, watch his gf makeup, he smile because he feel like she is really kind. he can't just tell her something that will make the girl in blue dress upset. so he give her the ring. You can see the girl hug YSH happily there but still he just hug her without feeling and other girl is finding his attention more. It tells the plot that YSH just don't love her. but he remain silence. The gf in blue know, but she pretend to be happy.