If I get it right, Ageha has known Takuto for 5 years, and as Yuuichi said, Takuto has known his current wife for less than that 5 years. So Takuto was dating Ageha, and then he cheated on him with his current wife, Ageha accepted it (because they're both guys, and maybe he thinks that they don't have future anyway a.k.a. having a family, that's usually the thinking that happens in yaoi manga), but at the end he ends up marrying her, but that bastard still wanted to continue with their relationship, and Ageha loved him too much, so he continue with it even though he doesn't like affairs (because when Yuuichi told him that affairs made him sick, Ageha agreed on that, and since Ageha is always honest and blunt I believe he was telling the truth).
I really hate Takuto.
Yes I also think Ageha was telling the truth and the thing that brothers me the most is that Takuto's behavior he's acting like he has done nothing wrong lile fuck you Takuto
Why does all the mangas i am recently reading have all douchebag cheaters!! Takuto is a bastard! This fucking cheaters they all just deserve to go to hell!