Uhh his brother was like a parent because his parents were never around. It IS possible to love your brother without it being romantic you know...Tengoku brothers’ relationship is a parallel to Aoki’s complex relationship with his mother. There was no indication of Tengoku loving his brother romantically.
I dont think he was in love with his brother beyond familial love. His brother was angsty and jealous of him doing well and felt inadequate and told manabu he hated him which I guess that 1 time was enough to break him completely
http://www.mangago.zone/read-manga/oni_to_tengoku/nbt/e3a5c2fa847cb178a5995ed7566e1a6f_chapter-10/pg-33/
"No matter what you can never be the number one of the person you love the most" isn't a feeling you normally have about your sibling. And it's not the only yaoi to have this plotline. Off the top of my head, Hidoku Shinaide has an identical plotline. He literally sleeps with his brothers partners so that they his brother can't love anyone other than him. I'm fully aware its possible to love your sibling without it being romantic. It's not like I came up with this idea, its in the story.
He is not just a normal brother. Basically his brother is practically his dad and mom. Tengoku was practically raised by his brother because of his parents, Obviously the person you love the most in the world are your parents before you meet your partner that you truly love or have children. He feels betrayed because the person who claimed loves him the most told him he hates him and wishes he never existed. Imagine your parents who always said they loved you say they hate you and never wish you existed one day. That is the kind of shock Tengoku went through. His idea of love is screwed up because he wasn’t able to recieve it from his parents and pseudo-parent (brother). Him sleeping with his brother’s lovers are an act of revenge and “tantrum” of a kid not getting attention from his “parent”. So far, nothing seems out of familial love for me. It seems to be case of brother complex.
From the statement “no matter what you can never be the number one of the person you love the most”, the stress is on the fact that Tengoku look down on love because he cannot achieve it since no one loves him as number one not the fact the that it is his brother that is not returning the love. From the overall theme of how childhood trauma from family shapes and affect the view of relationships even as adults, I very highly doubt it is romantic love. Hidoku Shinaide and this manga are on a completely different plane.
I think that's definitely one way to look at it, just not how I read the situation. Maybe you wouldn't describe it as romantic love but it certainly goes beyond familial love, but nobody has to read the same story the same way. We'll find out in the next chapter whether or not that's how he feels. and no big if i'm wrong.
Ugh I live for this manga but did he have to be in love with his big brother? This has been so different until this very moment!!