There is nothing pleasant about that, and he won't be able to bring himself to believe otherwise again. It's an abyss which only deepens as he comes to realise that he almost dragged someone else down with him - Harry was never a perpetrator, ever. He wasn't abused in a different, similarly bad way to Scorpius, but in exactly the same way and beyond. His body had been possessed, and he had no power to stop what was taking him over; all he could have done was watch helplessly as he did the worst, while the worst was being done to him.