Looking at how ANTI P.T. went... he really might end up with the black haired guy. On the other hand, the red haired one is getting a lot of screen time (as of now). I really can't predict this story.
However, the MC being in denial over his feelings just screams for an ending in which he finally admits them without shame. This could happen after a phase of discovering himself in a relationship with the black haired guy and realising what he "really" wants. As others have already stated, it would basically be like "Love or Hate".
On the other hand, he could fall in love with the black haired guy, after realising with how much respect and care he is treated (he clearly paid attention to MCs boundaries) in contrast to how the red haired guy treats him. A "Is that how being in Love is actually supposed to be like?" type of feeling.
There's a similar story to this where the ml ended up with his stepbrother. I'm getting the same vibes as that one tbh. I'm voting black hair, but red head has childhood friend plot armor and literally a genuine conversation about feelings and a redemption ark 50-60 chp later he's pretty much the winner. Good writing when readers are left guessing
The seme accepts boundaries and is caring... I want to read more of this! (≧∀≦)
Truly rare in Japan