No, you kinda got it wrong (but i might also got it wrong that you got it wrong lol). The 3 years thing was the uke answering the childhood friend that they (he and the seme) started dating in high school but changed mid-sentence that they officially started dating 3 years ago, around the wedding time if my timeline is correct. This is the flow of their convo:
Childhood Friend: I see.
Uke: You aren’t really surprised. Did you notice?
Childhood Friend: I might have. Rather, since when [did you start dating]?
Uke: Sine High Sch— From 3 years ago.
CF: Then I maybe not.
The CF meant that he actually noticed that they kinda have a relationship since high school but then the uke saying that they started dating 3 years ago doesn’t match the CF’s observation, when they started being close during high school. Hence, the last answer that he maybe did not actually noticed. And that’s why, we first got the flashback of when the CF noticed the change on the said uke and then followed by the present time. Nice flow, actually. I hope this helps clarifies it.
Am i dumb or are the years just confusing the hell out of me? The seme says he is nearing thirties and then in the extras where the childhood friend gets a kid he say he noticed uke and seme were dating in highschool itself 3 years ago?? Like am i just dumb omg? Anyways I enjoyed reading this. Very realistic rather than making the childhood friend be the ml