Why does Saul return to St. Jerome’s when he leaves the treatment centre?

Saul returns to face his past... although the school closed down years before, returning causes repressed memories to burst forth in Saul’s mind. It's at this point that Saul realizes that he was sexually abused and raped by Leboutilier repeatedly while he was at St. Jerome’s. He then remembers the different ways in which he tried to suppress the memories of those abuses even when he was still at St. Jerome’s.