Because Miyama is using Odagiri for sex and ignoring his feelings. Miyama is allowed to explore his sexuality, but using someone is wrong. He choses to ignore odagiri's feelings and thays wrong. Instead he should distance himself from him to not lead him on. Luckily Odagiri did that part himself to protect his peace.
Idk it's kinda complicated here since both of them consented to have sex and ended up being fuck buddies. From the get go, there was no feelings involved. If the seme wanted to, he should have also communicated that part. It may be hard since he has trauma from the past but hey, people aren't mind readers and as I've said communication is important. I hate how uke was invalidating women's feelings for the most part (which is wrong) but going back to my point he was exploring his sexuality and I think it's not his whole fault with how there is a misunderstanding between him and the seme.
god hes such a toxic twink the way he acts like his feelings are more important than anyone else's and acting like he knows better than the mf guy himself how hes gonna act. Odagiri doest deserve love, at least not until he changes as a person and fucking apologises