I think it’s more like they remembered parts of themselves they forgot they had when they met up again so to me it’s valid if they managed to get together and get past the work ha relatonship issues and finally be happy together since they are still into each other and honestly their personalities didn’t change much in those 6 years. Also, it wasn’t just natsuo’s fault about the no confession then not contacting for 6 years. Even if he got the balls to reply to issei’s confession a week later, he wouldn’t have been able to cuz issei cut off all contact and all marsupial knew was that he was somewhere in Tokyo. If someone confessed to me and didn’t even wait for a real teply before taking off like that, I don’t know how much I would care to go after them vs focusing on my own future schoolwork and career. I’m not gonna upend it just bc they were selfish enough to cut me off on top of their parents and all, like bruh. They found each other again tho in a way that I think suited them bc they both put off relationship stuff and honed in on making their careers so their OG dynamic fell back into place well with the side of them that’s adulting.
I relate to natsuo so much cause you just have those moments where you start comparing yourself to others no matter how hard you try not to think about it and his crash out was valid too i mean he literally bottled up those feelings for a long time not saying that pushing issei was right but dude you can't just confess and dunk out for 6 years with no contact. I think it would be right if they'd not date each other cause they sorta like the old version of each other.