For anyone confused. Here's what I got

This is what I understand so far. Yahiro asked yukichika to film his book, because he wants to show his inner self of loneliness to the world. Kinda like saying I'm here, I exist. Yuki didn't understand this because he doesn't have this inner loneliness also the reason why yahiro approached him. Same for keito, there's something that makes him want yuki. Yuki still hasn't managed to film the book because he can't seem to express the emotions yahiro shows in the book. Keito might just be the one to make the film a reality since he's similar to yahiro in the way that they mimick emotions in situations (yahiro is just better at it) the past of this promise to film the book is shown in between the more he's with keito. Keito still not knowing his own feeling because he doesn't understand love since he's never received wants to know why he's interested in yuki. Yuki knows he can't get close to yahiro so he plans to do something with keito to understand their similarities. Though yuki also doesn't seem to like to express himself so he's avoiding meeting with keito until the aquarium scene where he ends up with no choice. Keito seems to know that yuki is avoiding him so he acts very natural to make it less awkward for yuki. Yuki can't seem to understand this and seems to want to understand him more than before. That's all for now XD