David Simmons "met" Brennan on an online chatting site and was supposed to meet her for the first time in a restaurant but was stuck in traffic. As she is about to reach the restaurant she is almost shot and despite Brennan's wishes, Booth brings in her date as a suspect by pointing out he would have known where to find her. After he is cleared, he makes plans with Brennan for another date.
He is last seen in the final episode, The Woman in Limbo. He approaches Brennan while Booth tries to hurry her along. He informs her that he has read her manuscript. Booth asks if he is in it, to which Brennan replies "no," but Simmons tells him "definitely."
He is not seen again after Season 1, and in the episode The Boneless Bride in the River, Booth implies he turned out to be a recruiter for a cult. Hence, Brennan broke up with him.