This is where we get the fairly brief description which is nearly all we have on Augustine's longest romantic relationship:
In those days I lived with a woman, not my lawful wedded wife but a mistress whom I had chosen for no special reason but that my restless passions had alighted on her. But she was the only one and I was faithful to her. Living with her I found out by my own experience the difference between the restraint of the marriage alliance, contracted for the purpose of having children, and a bargain struck for lust, in which the birth of children is begrudged, though, if they come, we cannot help but love them.We also hear a bit about Augustine's life as a hot shot young rhetorician. In addition to his Manichean beliefs, he falls into consulting astrologers frequently, in part to learn the auspices when he's entering major academic competitions. At one point, a magician of some sort offers to assure that he will win a competition, but although Augustine finds the idea that that stars and planets can influence worldly events appealing (and has no qualms about consulting astrologers and books of astrology) he recoils at the idea of the magician sacrificing animals to dark powers in an attempt to secure a victory for him.
After winning one of these competitions, he finds himself in conversation with a proconsul renowned for his learning. They became friends, and the proconsul tells Augustine that he really should abandon all this astrology nonsense. He provides several arguments as to why the stars and planets are not in fact able to control our fates, but Augustine is as yet unable to be persuaded, though he says these arguments remained with him and were instrumental in persuading him years later.
Augustine's major personal and religious crisis in this period stems from one of his close friendships, another young man who, like Augustine, was a Christian catechumen but had strayed into Manicheanism. They both now consider themselves much more philosophically and spiritually sophisticated than their Christian families. However, the friend falls sick and appears likely to die.
His senses were numbed as he lingered in the sweat of death, and when all hope of saving him was lost, he was baptized as he lay unconscious. I cared nothing for this, because I chose to believe that his soul would retain what it had learnt from me, no matter what was done to his body when it was deprived of sense. But no such thing happened. New life came into him and he recovered. And as soon as I could talk to him -- which was as soon as he could talk to me, for I never left his side since were were so dependent on each other -- I tried to chaff him about his baptism, thinking that he too would make fun of it, since he had received it when he was quite incapable of thought or feeling. But by this time he had been told of it. He looked at me in horror as though I were an enemy, and in a strange, new-found attitude of self-reliance he warned me that if I wished to be his friend, I must never speak to him like that again.After that, Augustine leaves the topic alone, assuming that once his friend recovers and is past the worry of a major illness, he'll come around. But shortly after this the friend takes a turn for the worse again and dies.
The Augustine who is a character in the Confessions, Augustine in his mid twenties, takes his friend's death very hard indeed, nearly to the point of despair.
My heart grew sombre with grief, and wherever I looked I saw only death. My own country became a torment and my own home a grotesque abode of misery. All that we had done together was not a grim ordeal without him. My eyes searched everywhere for him, but he was not there to be seen. I hated all the placed we had been together, because he was not in them and they could no longer whisper to me 'Here he comes!' as they would have done had he been alive but absent for a while.Augustine's description of grief is so familiar and so human as to be instantly familiar -- and yet, the authorial Augustine also has a critique of his feelings a decade and more before. Looking back, Augustine sees himself as having expected something more than human of his friendship. He expected it to be unending and eternal. In a sense, he expected it to be god-like. Now, to the degree that love springs form God and all true loves are modeled on God, this is well and good, but Augustine now reflects on how his young self expected a beloved friend to be with him always, whereas it is God alone who can say truly, "I shall be with you always."
Had he loved his friend in God rather than as God, the older Augustine sees, he would have understood, if still suffered from, the separation. It was because he lacked the understanding (something which, perhaps, none of us in this mortal life can have to its fullness) that he and his friend were still united in God that his friend's absence seemed so unbearable and desolate.
The edition I'm reading is the Penguin Classics edition of Confessions, translated by R. S. Pine-Coffin.
You can also access a full, modern translation of Augustine's Confessions by Alberet C. Outler online, courtesy of Fordham University.