I complimented Frieren with it's Anime original aditions. A Sign of Affection lliterally added the backstory of Shin, Emma & Itsuomi as anime original as they only adapted chapter 13. fukking insane.
Unlike Rin and Kyouya, seeing Emma and Shin possibly together is going to be a tough and complicated road. Shin despite being popular with the girls, just not as much as Itsuomi obviously was more of a loner, quiet type. But man that scene which slowly went from darkness among Emma and Shin to sun shining on them exhibits how Shin fell in love with her.
But Emma being so driven in love with Itsumoi was something that would always hold him back. And this line
he says here doesn't do any favors. This is where Itsuomi unique way of communicating with other unintentionally causes Shin suffering. Because oh sure he will eventually to start dating, and he will be interested in Emma. And as a friend he doesn't want to take that possible happiness away from her. Thus, we also see him having girlfriends as they ask him out, but they can easily tell his heart belongs to Emma.
But for Itsuomi it was more so finding the special girl for him, which is Yuki. Shin is unable to say the truth simply because of how much he loves Emma. It's a conflict you can empathize because you know the truth will crush her. But isn't it more painful to not let her know and in consequence you are suffering too?