If you could sum up our hero in one word, it would be "anticipation." This guy will do anything to find fulfillment in the form of seducing Madame Arnoux. Imagine spending twenty years just to get someone to say yes to a date. Frederick is constantly in preparation and ambition mode—so much so that he hardly ever slows down to appreciate life and all of the bourgeois luxuries he has. Or to crack a book, for that matter. After all, he is a law student, a fact that is easily forgotten given that he spends so much time listening to his friends debate "Destruction of Privilege, Monopoly, Hierarchy, Authority, the State."
After he meets Madame Arnoux, Frederick spends a lot of time in lala land. Everything seems to remind him of her. "Oh, look at the lamp post; she likes light. Oh, look at that woman; she's a woman, too. But that woman is not she. The cruelty of it all!" (Note: not a direct quotation.)
This book could just as well be titled Frederick's Frustrating Follies. He spends so much time in despair over the fact that Madame Arnoux doesn't love him, that he is not rich enough, that his friends debate politics too much—you name it. It's funny because the one person who is not standing in his way is Monsieur Arnoux. He's so busy partying and messing up his business that he doesn't seem to care that Frederick is chasing his wife. (Just accept that everyone has affairs here and move on.)
This phase plays out in a strange way in Sentimental Education because Frederick shares a brief romantic but strictly emotional bond with Madame Arnoux, and then it all goes south. He is in deep despair—a mood that is reflected in the revolutionary chaos playing out all around him in the streets of Paris. In response to the nightmare (though he does inherit a sweet fortune from his uncle), Frederick gets into all sorts of entanglements with other women (Louise Roque, Madame Dambreuse, and Rosanette). At one point, he's sort of engaged to two different women and has a third one pregnant. There's some serious juggling going on here.
The destruction happens to Paris—literally—but Frederick implodes in his own passive way, too. He responds by traveling. Ah, the life of the rich. Everything culminates when he gives up his one shot with Madame Arnoux and realizes that the best times of his life were at a brothel with his best friend, Deslauriers. Ick.