imo the answers are kinda like
because he likes him
he doesn't really switch personalities imo
because he likes him and doesn't want him to find out/ soil him or smth
I didn't really get the question
of course this is only what I got, I may be wrong
I agree, I read between the lines and I got the same conclusions as you. What I actually meant is: these are not good motivations at all. For instance: uke realizes somewhere along the way he likes seme, so decides to turn a 180 degree from when they were children and not only become a deliquent, but also actively ignore/hurt his childhood friend. Why? In the first place, what led him to become a deliquent to the point he would become a "bad influence" to the seme, or even a danger to him? More than that, why is he taking the responsibility of protecting his friend's reputation? He claims he is pushing the seme away for his own good but, again, what is he protecting so fiercely? Because the seme's family seems to cheerish their friendship, and so does the uke's own mother. In fact, it seems keeping the seme away is causing him more pain than keeping him close would. All these questions could easily be answered with a "because he likes him and therefore wants to protect him", but you get my jam, both of them are taking EXTREME actions towards each other, that motivation is at best lacking and at worst nonexistent ╥﹏╥
(Oh, the last question is basically: if that dude is such a bad yakuza guy, he could very easily pay for a young sex worker boy. He literally didn't have to go after a random high schooler, who could pretty much call the cops on him, to sexually harass and rape him. It's just too much trouble/danger. Again, his reasoning could be "the uke is my type and I really really want to bang him". And again, really weak motivation)
If I could chime in~ Atsu (seme) and Touma (uke) liked each other since they were children. Since Touma was little, he always felt he wasn't normal and he picked fights with older opponents and Atsu was always by his side to look after him. My guess is that Touma is badly coping with his feelings for Atsu because he doesn't want to "taint" him. He wants Atsu to have a normal life, normal marriage, etc. He participates in fights and became a delinquent as a way to cope with these feelings and to push Atsu away~
Atsu just wants to be with Touma (he always had since they were children), and after being mentally cornered by Touma's indecisiveness and getting mixed signals from him, he ended up forcing Touma into a sexual relationship~
I think the explanation for the first part is what @Shiragiku said but I have to agree with the yakuza one, his reason is too weak for the risk
Although I AM sticking around until the end of the story, this manga is definitely very confusing. There are no motivations for the actions of any of the characters - why does the uke accept the seme's behaviour? Why does the seme switch personalities without any warning? Why does the uke start avoiding the seme to begin with? Why does a random yakuza guy want to rape a high schooler, even going through the tremendous pain of blackmailing him? This story feels like it's lacking an entire volume of background and character development to get to the point they are now. Nice but kinda lazy writing tbh