For me is more like he knows he is playing with the semes feelings and not telling him "hey I'm having sex with others" but then again the semes love for him is blinding him from the truth. Them being sex friends is not gonna work since the seme has pure feelings for him. I say they split up and do what they want, the uke sleeping with who he wants and the seme finds somebody else that wants to be in a monogamous relationship with him. But you're right he shouldn't be slut shsmed.
I have no issue with people's sluttiness. But this uke makes himself very hard to be liked. I mean, sometimes, it is not wrong to do something does not make it right.
I really dislike the way he acted. I mean, he seemed not to want to have sex with his ex? If so, what the fuck did he do despite of not wanting it? Or he actually longed for sex, then don't fucking feel bad about it. He acts so bitchy, I am speechless. I haven't seen any single act that can show his tiny little bit love to seme. He is more of a sex toy than a human being to me based on what I saw.
You know what, I am probably too serious towards this manga because it seems that the author does not care about if it makes sense at all.
It's not, they're not dating, they're not exclusive they're just sex friends. As for hating on him bcs he likes sex, why? He has a high libido no shame in satisfying it.