Both of them are heavily affected with the whole "pedophilia" incident. Kei, or nii chan knows that his actions permanently removed all of yui's future, he knows he's responsible of turning yui into who he is now, but he still believes that yui could've turned normal if it wasn't for his selfish needs of having someone who understand his situation. Kei needs to take pills after sex because of PTSD, he gets anxiety that after they do it, yui will leave him and turn back to being 'normal' like what happened to his ojii chan. Yui takes pills because he is stressed over the idea of being normal or being with nii chan. He doesn't want to throw away his family like what kei did, and he can't bc he's still a university student. He takes the pills to get him from dressing out that "his relation ship with nii chan is fucked up and he does not know if he truly loves kei" but is dependent on the sexual aspect of their relationship. Both of them are addicted to the idea of being in a euphoric relationship, but are in constant anxiety from the PTSD, the fear of the world knowing, yui's parents separating them (or yui's fear of being separated from his family/being seen as normal)
my prayers have finally been answered! Thank you
OMG THANK U I WAS SO FREAKING CONFUSED
what was the ending? he is getting nii-chan addicted or are they both addicted? and they both die from drug overdose?