Augustine is well known for lamenting his years before he became a Christian. He seems overly rocked with guilt over his sexual escapades.
As a young, Well to do intellectual in college he did with a lot of men did back then, which is to take a concubine. He fell in love with her, and they had a child together but because of her lower social class he was not allowed to marry her. After he became a Christian, it deeply wounded his soul that he could not marry her, and that he had sex with her outside of marriage in the first place.