Why is the Self-Taught man thrown out of the library in the novel, Nausea?

On Roquentin's last day in Bouville, while he is at the library, the Self-Taught Man is caught making sexual advances toward a young schoolboy. The Corsican also sees this, and he yells at the Self-Taught Man and punches him in the face, causing his nose to bleed profusely. The Corsican tells him to leave the library immediately and never come back again.