In early chapters there is an "ark" where MC is at home ill, and people come visit him, one of which gives him a kiss on a cheek IIRC, its drawn in such a way that it suggest Takt being that person and thus making him "gay", which was later supported by Takt weirdo behaviour and various scenes, including the reason why he broke up with Umimi, etc. Thou like next chapter kinda suggest it was Umimi who kissed him, thou if you wanted, you could interpret it as her seeing Takt kiss MC or something.
Either way the kiss thing was one of the things thanks to which people were so sure early on that the big secret is Takt being gay and in love with MC. But it doesn't really make sense with all the chapters that are available now.
Also in that post I reacted to you wrote that Takt is to nice towards MC suggesting gayness, but I fail to see it. Takt looks shady all the time, he makes faces and behaves like typical NTR manga character who preteneds to be your friend, but behind your buck fucks and steals your girl.