In the book: Bill, Elena's husband, is a practical, relatively sympathetic character who has a more benevolent relationship with his daughter, Izzy. As a defence attorney, he agrees to represent the McCulloughs in their legal case against Bebe, but eventually struggles to decipher right from wrong when the line of morality blurs.
On the show: He's not all that different from the book (except, the novel doesn't give us a visualization of *that* underwear scene). You can tell he grapples with the unsteadiness of his family and doesn't really know how to deal with Elena's sanctimony. The scene of him standing in the rain, begging Elena not to go to New York to investigate Mia (and, as he correctly presumes, visit her ex, Jamie) is a very telling portrayal of their marriage. One minute, you don't like Bill because he's working as the McCulloughs' lawyer and contributing to the polarizing custody battle, then the next minute, you feel bad for him because Elena is a handful.