i love angst's Things

so i was trying to find this manhwa, i forgot when it was released but it has too small fandom. there's a little brother that's like got a bipolar disorder and got something in it, hes a bit crazy..his hair is black i think and the mc is red haired the big brother.. the little brother also has killed his pet, golden fish pet like that..and he's a bit obsessive (?) to his big brother..! its not incest, its like a psychology manhwa. the little brother in the end got into mental hospital if i remember it right and he still hallucinations that his big brother visited him constantly. i think the big brother is dead. please help..!