I think he simply despised the choices he made before he gave his life to God and he moved in a 360 direction. Unfortunately, this was before AA and he might not have realized that sex didn't have to be something *everyone needed to avoid. Maybe he actually did need to avoid it. Maybe it was a problem in his life. For him it had been carnal... he needed to know the pure side of it, the intention God designed it for.
Agreed. He was a man of intense choices, but felt his sexual urges were difficult to control. I think his time with the Manichaeans also greatly influenced his body/spirit dualism and his theological success against the views of Pelagius probably made all his other views (including sexuality) more credence. Furthermore, if it wasn't for Saint Augustine, we probably wouldn't have the concept of Original Sin, as we do today, which is highly sexual in nature and form. So....thanks a lot buddy.