Who is Shep Campbell from Revolutionary Road and what is their importance?

Shep Campbell and his wife were the Wheelers' neighbors. He also plays in the community theater production with April, during which time, he becomes infatuated with her, especially after the two couples go out dancing together. Later, as the Wheelers' marriage becomes more unstable, Shep and April indulge in a one-night-stand. Shep becomes convinced that he is in love with April, but she brushes their encounter off as nothing more than it was.... sex.