I don't really understand his brother's real intention why is he so obsessed with uke??? A...

Well, based on the last chap, when they were kids, the mc is the only one who shows concern to him when he was getting bullied. So I think that made him obsessed with his savior? I dunno. (=・ω・=)

maybe they were just acquaintances because sometimes translators translate the word as brother instead of hyung? i'm not sure thought. (hyung is a male older than themselves)