
He didn't exactly remember, he just kept getting unexplainable emotions towards the uke and being haunted by his ghost-self. He finally understood the ghost kept showing up as a way to tell him to stop worrying about what the truth was and to just go with his feelings.

It seems like he was having dreams about his time with Iku (namely the time they had sex when he was still a ghost), and he couldn't understand why he was having these dreams. He seems to start feeling that what Iku said (about them staying together when Mimori was a ghost) is true, and even starts seeing his own ghost. I think him seeing his ghost was kind of his mind's way of accepting the situation, and thus being able to rationalize the residual feelings he had for Iku. I also think he was rejecting Iku previously because Iku was stuck in the past. He wanted a part of Mimori that Mimori could not give him anymore, which is why he stressed that he wanted to think about the future with Iku in the later chapters. Hope that helps, but then again the translations had me a bit confused as well.
i didn't understand half of these chapters.
i don't know if it's because of language, or author wanted to be more "deep" and i didn't think enough about it, but it's still cute ╮( ̄▽ ̄)╭