I think the reason why Haruki is starting to crave sex is a result of the Post Traumatic Stress Disorder (PTSD) he developed after being raped by Hikaru. Hypersexuality is a very common coping mechanism for people who have been raped, but it's mostly used as another form of self-harm. It's a vicious cycle, because having sex is the only thing that can distract him, but through doing it, he only hurts himself more :(
Another good explanation
I dont think that he exactly hateshikaru, i think his brotherly love is realy strong and he cares about him, i think besides rape this is what broke him, the fact that their sibling relationship turned out that way. Also i think his body got addicted to sex or something like that while his mind refuses enjoying it and this is his another personal conflict. Also i think he lets hikaru rape him over and ver again only because this is the way of self harming, his mind and soul is shattered into pieces. About killing part, haruki knows that no matter where he goes Hikaru will find him so there are two possible ways to end this first by killing his brother, which he cant do because well not everyone is capable of killing someone, and another solution is to commit suicide which he does. I find little brother really pitiful, you can see how damaged and wrecked peronality he has, but for me his actions, even though they were because of "love" are unforgivable, he really is monster
You know he wanted to kill him and he was about to but he thought Hikaru's only fault was just because he took a liking to him like he said in this chapter. And you see after thinking like that he stopped
He wanted sure but couldnt and i think his way of thinking was really stupid, he kinda justified all the things Hikaru did to him, but i think that way of thinking was just excuse to not kill him, very stupid one in my opinion, but in his state of mind and after all that hes been through looks like he just can think straight anymore maybe , dont know, but for me hes that kind of character that is not capable of hurting others and thats why he couldnt do it. But how he justified Hikaruli really pisses me off like reaaaallyyy
I thought he hated Haruki for all the things he has done to him, but when he says his body and mind are jumbling, he is implying that sex feels good even thought he hates the lil bro? I kidn of got confused in this cahp, 'cause he practically let lil bro do whatever he wants with him, says it will be easy to get rid of him but can't kill him? Lil bro is way too creepy. I feel sorry for Haruki :(