The founder of a Texas megachurch has resigned in the wake of allegations he sexually abused a girl during the 1980s, starting when she was 12, according to a report Tuesday. A spokesperson for the Gateway Church said pastor Robert Morris, 63, didn’t provide church elders with “all the facts of the inappropriate relationship between Morris and the victim, including her age at the time and the length of the abuse,” the Dallas Morning News said. “The elders’ prior understanding was that Morris’s extramarital relationship, which he had discussed many times throughout his ministry, was with ‘a you…