If you asked Saruman why he fell, he would have claimed it was because of love.
For Curumo had loved once. Her name was Yávë, one of the Maiar of Yavanna. She had been beautiful to his eyes, her her fána with its long, curly auburn locks, and those bright green eyes that revealed the stunning shade of her fëa. She was high summer to Curumo, those long days just before autumn came: and he loved her. There was nothing that could take her away from him, except herself. Not even his rival Mairon could think to take away her love like he took everything else Curumo wanted, for Yávë was as old as he was, and would never look at an obvious child like Mairon.
But he never could quite bring himself to tell her. Her oldest sister Palúrë, who always reminded Curumo of winter, was espoused to his oldest brother Nyeleccaner, and so he saw his lovely Yávë often. But he could never quite be sure that the affection she showed towards him was more than simple sisterly concern.
And then disaster struck. Yávë was captured by Melkor, and Curumo was frantic, heading out with his younger brothers and all the other Maiar who were sent hoping to find her. Find her they eventually did, but it was too late. Her spirit had been dimmed and broken, and she was little better than a shell of the bright, vivacious Maia she had been.
Yavanna was heartbroken, and she and the other Valar attempted to heal the damaged Maia. They succeeded, to a degree: Vávë regained her light and happiness, but the cost was her mind. Now little more than a child, she played happily at Yavanna's side, but those who had known her still mourned. Curumo could not stand to be near her any longer, for all it did was remind him he could never have her now. His love darkened, and he began to hate the Darkness that had destroyed his beautiful Yávë.
His jealousy for Mairon also grew apace, fueled by his rivalry and his belief that the younger Maia's life was so much better than his own. His dislike for his fellow Maia bordered on hatred, and as his older brother was Aulë's chief Maia, Curumo had the power to make Mairon's life miserable, which he did, rationalizing it in his own mind as 'equaling the score'.
And then it was discovered that Mairon had betrayed them all, that he had been the traitor that had caused so much trouble. Curumo was convinced that it was all to mock him, that Mairon was siding with those who had destroyed Yávë to flaunt Curumo's loss in his face. He continued to express his distain for the younger Maia, even as Númenor was destroyed, and most of those in the west began to hold Sauron, as he was now known, in a horrified awe.
Then came the day the Valar decided in council to send representatives against Sauron who was again rising. Curumo was the first to step forward, eager to humble the Maia he had long hated. To his annoyance, he was given companions, useless Aiwendil by Yavanna, and Alatar and Pallando by Oromë, who would travel into the far East where that Vala had once ridden extensively. But they were merely nuisances. It was when Manwë proposed to send Olórin that he wanted to protest. Why send the older brother of the Maia they were being sent to destroy? For all anyone knew, he would sympathize with the miserable brat, and doom them all!
But Curumo pushed it out of him mind. It would not matter, for by any means necessary, he would humble Sauron, and avenge his lost love.
Well, one day a lot of the stuff here will be woven into a longer story of mine, but it's rare for Saruman to actually talk to me, so I had to write it. And Crackers wanted to see it, so I'm posting it... Anyway, I hope you enjoyed it. :)