When thinking about Giovanni, it's important to remember that the story is narrated by David. So everything we know about Giovanni is what David thinks about Giovanni. When he recalls how things happened with Giovanni, things unfold as David remembers them. The point is that the Giovanni we think we know by the end of Giovanni's Room is really just David's version of Giovanni.
That's not to say that David is intentionally lying or misrepresenting Giovanni, or that Giovanni is not a character in his own right. But perspectives can be distorting, and perhaps nowhere can they be quite so distorting as they are in the case of a love story. David both loves and hates Giovanni. So the image of Giovanni that we get in the book is, to some extent, nothing more than a fly that is caught in David's narrative web.
All we know about Giovanni when we first meet him is that he is an extremely attractive Italian man who is living in poverty in Paris and has been taken under Guillaume's wing. Yet, very early on in the story, David makes it clear that Giovanni is in pain. He remembers Giovanni saying, "This dirty world, this dirty body. I never wish to make love again with anything more than the body" (1.2.11). At other points, David talks about Giovanni's inner struggle and how, when he doesn't know that other people are looking, one can see the anguish on his face.
Giovanni's Room is full of mysteries, many of which are layered on top of one another and intertwined. Obviously, the big one is why Giovanni is going to be executed, which we don't learn until near the very end of the book. Another huge one, though, is why Giovanni is in such torment. The two are, in a way, woven together, because whatever caused Giovanni such pain is what ultimately put him on the desperate path that will lead to his execution. Based on the limited information we have, though, it seems that Giovanni is living a pretty hedonistic life in Paris. When David refers to Giovanni's inner pain it might be hard not to think of Giovanni as a drama queen.
There are certain hints that crop up throughout the story. One is how close Giovanni clings to David. David remembers how Giovanni "told me in many ways as he could find how wonderful it was to have me there, how I stood, with my love and my ingenuity, between him and the dark" (2.2.11). Another one that is more confusing is Giovanni's hatred of women. When David and Giovanni discuss women, Giovanni's opinions are almost shockingly misogynistic. After confessing to the fact that he would often beat women, he confesses, with great understatement, "I perhaps don't like women very much, that's true" (2.1.26). For the most part, Giovanni seems to be a gentle creature, so the reader can't help but wonder what caused this sense of violence and hatred.
When David finally breaks with Giovanni, the reader finds out. Giovanni, in tears, admits that he was married back in Italy and that he and his wife had a child together. But "it was dead, it was my baby and we had made it, my girl and I, and it was dead. When I knew that it was dead I took our crucifix off the wall and I spat on it and I threw it on the floor and my mother and my girl screamed and I went out" (2.3.194). The passage is heartbreaking, and it explains a great deal of Giovanni's behavior throughout the story: his sense of desperation and flight; his fear of being alone; his intense anger towards women, optimism, and God.
There's something interesting here about how David narrates the story. The story is told in the past tense, which means that from the very beginning David already knows what is going to happen. He could tell us all about Giovanni's past on the very page of the book and explain why Giovanni behaves the way he does from the start of the story. But he doesn't. Why?
Well, for one thing, David re-tells events as they happened. He went through a period where he didn't know what was bothering Giovanni, and so he forces the reader to go through that period as well. What is more interesting, though, is that he forces us to feel what Giovanni felt. What we mean is that Giovanni was in an intense state of denial. He was in flight from his past and wanted to think about it as little as possible. If he could, he would probably pretend that it had never happened.
By having the past suppressed, then, the reader is put into a situation much like that of Giovanni's. We are forced to empathize with him because the source of his pain is denied expression, and we are made to feel his suffering without being allowed to face the event that caused it.
When David meets Giovanni in Guillaume's bar, Giovanni seems like a confident young man. He handles Jacques's advances easily and is remarkably forward with David when the two of them begin flirting. Though Giovanni teases David about being a philosopher, it is clear that he has worked out his own philosophy. It's a cynical philosophy that suggests life is hardly worth living, so one might as well try to get pleasure while one can.
Giovanni is given to expressing his opinions in bold terms. From the start, he teases David about his American optimism, and when David speaks of choice and free will, he says:
Time is just common, it's like water for a fish. Everybody's in the water, nobody gets out of it, or if he does the same thing happens to him that happens to the fish, he dies. And you know what happens in this water, time? The big fish eat the little fish. That's all. The big fish eat the little fish and the ocean doesn't care. (1.2.103)
David is not as confident as Giovanni and, at the time, he also isn't as comfortable with his sexuality. In many of their arguments, Giovanni clearly maintains the upper hand. The only way that David can stay on an equal plane with him is by being reticent and withdrawn. When David reveals that he is a bit ashamed of what their relationship and says that it would be a crime in his country, Giovanni says, "If your countrymen think that privacy is a crime, so much the worse for your country" (2.1.46). It's hard for David to argue with Giovanni because he constantly has to put his real problems in other terms. The simple fact is that he is afraid of what is going to happen between them, and he constantly has to make flimsy excuses to maintain his distance.
Yet Giovanni is not as confident as he seems. As we discussed in the above section, Giovanni is also running away from a part of himself. Whether it's immediately apparent or not, Giovanni's life has become a downward spiral of self-destruction. His relationship with David might seem to hold off his impending doom, but they both know that the relationship is only temporary. What gradually becomes clear is that Giovanni's confidence is simply a dam that he has set up to keep from drowning in the misery of his life.
That said, Giovanni is much more open about his emotions than David is. Before David leaves, Giovanni says, "You want to leave Giovanni because he makes you stink. You despise Giovanni because he is not afraid of the stink of love" (2.3.202). David, by contrast, is terrified of "the stink of love." Not only is he ashamed of their physical relationship, but at no point in the story is he willing to make himself vulnerable. He takes no risks in his relationship, and in the end he gets no rewards.
There is perhaps no moment at which Giovanni is more honest than when he says, "Maybe everything bad that happens to you makes you weaker" (2.3.23). The statement might not stand as an aphorism (a general truism), but Giovanni is alone; he lacks support or real friends or encouragement. And sadly, in this case, Giovanni is absolutely right.