I think it's important to note that Tasuku's story isn't being left unresolved here. Everyone has an arc and a conclusion to that arc. Tasuku's conclusion was him deciding to accept that the future is unknown, and trying to pursue the knowledge of what it will be is pointless. At the start of the manga he thinks his life is over. He thinks he knows what the future will hold. He sees a run-down, abandoned house. But then he pulls out the first nail and takes a step towards a different future; one that he can't see, just as he can't see what that run-down house will become.
He keeps trying to fight his own emotions by holding them in, telling himself that if he breaks, it'll all be over, and his future will be set in stone. He even thinks that Misora should decide what his future will be. When he finally does break and confess, nothing changes. His future is still just as unknown as it was before, and he doesn't understand why his relationship with Toma hasn't changed.
It's Anonymous who finally makes him realize that being unsure of what the future will hold is fine. He spends the entire manga wondering what kind of person she is. When he finds out she's asexual, he asks how she can be sure that she'll be single all her life, but even she admits that she doesn't know. She outright tells him that she doesn't know who she is. He doesn't want to lose sight of her through her becoming this unknown entity, but with her not knowing either, he decides that her real is all that matters. She is (metaphorically)his future, and as long as he can see his future, he doesn't need to know what it will be.
It should also be noted that Chaiko sees the same vision of Anonymous jumping from the railing that Tasuku sees. In his case, he has lived his whole life fine with the future being unknown, but when finally confronted with the eventualty of finding out what it is, he turns away, not wanting to be a part of it. He doesn't want to watch his partner die, and he doesn't want a connection with his partner's family. Anonymous has to give him a literal push to accept that what he sees needs to happen.
This really is a masterpiece.