Clay Pigeons (1998)

What it's about

Clay is a young man in a small town who witnesses his friend, Earl, kill himself because of the ongoing affair that Clay was having with the man's wife, Amanda. Feeling guilty, Clay now resists the widow when she presses him to continue with the affair. Clay unknowingly befriends a serial killer named Lester Long who murders the widow in an attempt to "help" his "fishing buddy."