Besides, he perceived in the treaty the end of his hopes of a descent upon Florence, which was the cause of all his labours.

So he rejected it.
But Valentinois had already got the Orsini and Pandolfo Petrucci on his side, and so the confederacy was divided.

Another factor came to befriend the duke.

On November 2 he was visited by Antonio Galeazzo Bentivogli, sent by his father Giovanni to propose a treaty with him--this state of affairs having been brought about by the mediation of Ercole d'Este.

From the negotiations that followed it resulted that, on the 13th, the Orsini had word from Cesare that he had entered into an alliance with the Bentivogli--which definitely removed their main objection to bearing arms with him.
It was resigning much on Cesare's part, but the treaty, after all, was only for two years, and might, of course, be broken before then, as they understood these matters.