I believe from some other summaries people made about spoilers: the reason why he left was due to work/dad/etc. I don’t remember the exact reason but the uke wasn’t the actual reason he left. He did leave the uke hanging with the sort of vague relationship he had because at the time I don’t think the seme even understood what his sexuality was. I guess you could say that afterwards, he kinda realized that the uke was the reason why he realized he’s gay. And over the years went with dudes for partners. There was some communication issue going on, and eventually the seme forgot about it. Until the uke showed up again.
The uke was always a very kind person if you remember the talk him and the seme had over his ex or just lovers in general. And it was implied that Uke wouldn’t care and would naturally forgive them (something along the lines). The seme never did cheat, although he had lied about some things, none were TOO damaging to cause them to not get back together. All the issues seme had were mainly just his past. The uke mostly had an issue with the fact that the seme was the same guy from his past that ghosted him. Everything else wasn’t really a problem. After Uke came to terms with that fact, and probs realized how sincere the seme’s feelings were- he forgave him.
BITCHES, IM CONFUSE. SPOILERS
So they met when they were young, and the seme was tutoring him and something happened and the seme left him or some shit. Then the uke was upset, seme gets abandoned for like 2days and somehow the uke just forgave him after the dramatic shit he had done. I'm legit confuse.