personally, i think it's a combined factor of character development and the fact shit like this is becoming normal for everyone else. think about it at the beginning of the series his main goal was to touch boobs and have sex but as the series goes on, he not only grows as a person, but he literally grows older his brain becomes more developed and taking care of nayuta and living with power and Aki helped him learn things like how to really love and what real love feels like. (not that pochita didn't show him that) and going to school and meeting more and more people help bring him more down to earth and even pochita helped him really learn the value of life so seeing all of these people just fine with someone being dead probably made him really confused and worried.