
I think that the uke could forgive the seme so fast because he need to, after all, he's complete alone (no Familiy and friends)
And he was once abandoned by a close person (father ) so he dont want to get through all this again.
Sure, he could take the offer and marrie the presidents daughter, but he may knew, that for a person like him (introvert and emotional injured) it's hard to get close to a complete stranger.
So he prefers to hold onto that twisted relationship with a person that loved him for a long time, even when this person is crazy.
Just my opinion.
Hope it's understandable
(Sry for bad english)

Somehow, it's totally stupid. What a mess: seme gave uke sex education, made him into a little slut, leave him for years, let uke had girlfriends and so on, uke couldn't have proper sex with girls, get back to seme, found out he (the uke) is gay and in love with the seme, seme teasing uke for whatever reason and now the uke had a relationship with seme's ex boyfriend. More a sope opera than a manga. So much drama and i love it. Even the people in there are hard to understand, at least it's funny.
I suspected the ex cop turn out to be a psychopath or murder, unexpected when it turns out quite normal
I red to much Killing Stalking and Harada
( ̄∇ ̄")
looooool
Hahaha, I totally get what you mean! (≧∀≦)