The Confessions is all about sin, which falls pretty nicely under the category of Actions (though it can also fall under Thoughts and Opinions too). There are a lot of different reasons why someone might commit a particular sin, but there is also the sheer fact that they sinned. For instance, Augustine might not be able to give a reason for why he stole some pears, and maybe if he was starving on the street we wouldn't blame him for it. But without a good reason, he's just left with the sin.
Sex and Love
You might think that we're just pointing the phallic finger at Augustine on this one, but he's actually not the only one whose sexual antics are detailed in the Confessions. For example, we know that his mother, Monica, is a devoted wife… even though her husband, Patricius, chases skirt all around town. We also know that while Augustine kept a mistress for ten years and fathered an illegitimate child, his friend Alypius has only had sex once. And he only did it see what it was like. (Sure, Alypius…)
So in the case of Augustine's parents, it's pretty clear who is being coded as Good and who as Bad. But in the case of Augustine and Alypius, we don't consider either one of them to be blameless. It's not like a gladiator addiction is all that flattering. In fact, Augustine seems to be a pretty loving father, and a loving partner to his mistress too, until he decides to dump her so that he can marry a (much) younger woman. And take another mistress in the interim. Ouch. This whole debacle makes us realize that Augustine cares more about status than love, and more about sex than any of it, so he kinda loses points with us.
Thoughts and Opinions
Sin can take two forms: you can do evil actions or you can have evil thoughts/beliefs. (We're looking at you, Manichees.) Because this is a work that's all about how Christianity is the absolute truth of the universe, we can immediately judge whether a character is going to be "good" or "bad" (we're using scare quotes because we mean good or bad according to Augustine's standards) based on what beliefs they subscribe to. Faustus? Bad for sure. Ambrose? Two thumbs up. Patricius? Bad news bears. Monica? Good to the very end. You get our drift.