A hundred, he said. Paul Pierce said yesterday that he has thought about his first game back in Boston a hundred times, and tears come with every visualization. Indeed, Brooklyn’s new small forward had to stop while telling this story to keep his voice from cracking. But Pierce also knew that it was time to accept a break in his 15-year association with the Celtics. He didn’t want to return to an organization focused on rebuilding instead of what he has known for most of the last five seasons. As harshly as reality hit him, he had to fight against those strong emotions that were already making him miserable. So when Jason Kidd, his old adversary and new head coach of the Nets, called to talk about the impending trade between the Celtics and Brooklyn, Pierce took the next step himself. He called Kevin Garnett in an attempt to talk his old friend into waiving his no-trade clause. The call lasted for approximately two hours, with Pierce outside on his cell phone in the 100-degree Las Vegas heat, and Garnett secluded in his Malibu home. By the end of it Pierce’s shirt was drenched. But he had made a very tough sell work.