Liar's Moon (1982)

In East Texas, the summer after high school, Jack falls in love with Ginny, the daughter of the town's banker (Jack's mom's high school sweetheart). Ginny's been at boarding school; she's headed for Vassar. Over her father's strenuous objections, she spends time with Jack. At summer's end, Jack and Ginny elope to Louisiana (where 17-year-olds can marry without their parents' permission), and he gets a job in the oil fields. Her dad hires a menacing private eye to find them, Ginny's pregnant, her town doctor gives her horrible news, and Jack's mom has her own agenda. It seems that Jack and Ginny have grown up under a liar's moon. What will these sweethearts do?