What did Jim mean. (Spoiler)

When Jim and George are in the car, Jim says something about the pain of loving someone you can't have....which George realizes Jim is talking about his mom, Rebecca. Then George asked if his grandmother had promised the mom to him and he replies something like "no, the preacher did". what did that mean??? I thought it was going to then show the preacher was evil, too...but that story line just dropped out.