Who is Matthias Berger from Floating in My Mother's Palm: A Novel and what is their importance?

Matthias Berger rents a room in Hanna's family home. He once studied for the priesthood but decided against it. Hanna notes that Matthias often has male company, occurrences accompanied by bruises. Hanna is too young to fully appreciate what is happening in his life, but the reader realizes that Matthias is accepting punishment for something he cannot control.