Friendship is really put to the test in Sentimental Education, and boy is that the case with Deslauriers and Frederick. The two boys met as kids in Nogent-sur-Seine, and though their lives and upbringings are worlds apart, they still have a deep connection. In other words, these guys are serious besties. Here they are making plans for the good life:
They spoke of what they would do later, when they had left college. First of all, they would set out on a long voyage with the money which Frederick would take out of his own fortune on reaching his majority. Then they would come back to Paris; they would work together, and would never part; and, as a relaxation from their labours, they would have love-affairs with princesses in boudoirs lined with satin, or dazzling orgies with famous courtesans. Their rapturous expectations were followed by doubts. After a crisis of verbose gaiety, they would often lapse into profound silence. (1.2.9)
But don't get your hopes up. Those were the plans, and as we know, in Sentimental Education, plans don't usually play out very well.
Frederick and Deslauriers actually get on each other's nerves all the time. Deslauriers, in particular, has some bones to pick with his pal. For starters, he's irritated by Frederick's obsession with Madame Arnoux (Frederick goes on and on about her and totally flakes on Deslauriers because of it, so who can blame him?). Plus, he's definitely a little jealous of his friend's access to high society, from which he is excluded.
One thing to remember is that it's only through Deslauriers's eyes that we're able to see Frederick's annoying habits. Everyone else seems to think he's kind of awesome, right?
Eventually, Deslauriers gets tired of watching Frederick have all the fun. He pursues a job that has been offered to Frederick and makes a move on Louise and Madame Arnoux. Whoa there, Charlie. That means the two men are now rivals in love—Frederick just doesn't know about it. And sure enough, Deslauriers marries Louise just as Frederick has decided to settle down with her. Then he goes on to become a pretty successful clerk.
So, did Deslauriers win that friendly competition? We're not so sure. At the very end of the novel, they reconcile and reminisce about their youth. The verdict? They've both acted foolishly. But hey, at least they have each other.