The Uke had his reasons for not continuing his relationship with the Seme, although it wasn't the best way to deal with it, but he was scared and wasn't thinking. As for the Seme, he properly broke up with his girlfriend before he even did anything with the Uke. Also, being clingy isn't always a bad thing and the Uke didn't seem to have a problem with it. Therefore they are both not horrible people. They just make mistakes. But also its just a manga with fictional characters so its not something to be so upset about.
His reason wasn't enough to run away or to have sex with another men
couldn't get past the end of chapter 1: the uke is a heartless fucker and the seme is a clingy idiot and he even has a girlfriend yet he is chasing a cruel man's ass. Worst match ever or maybe best match since they're both horrible with the uke being a few steps worse