(a) A person commits adultery when he engages in sexual intercourse with another person who is not his spouse and lives in cohabitation with that other person when he or that other person is married.
(b) A person does not commit a crime under this section if he reasonably believes that he and the other person are unmarried persons. The burden of injecting this issue is on the defendant, but this does not change the burden of proof.
(c) Adultery is a Class B misdemeanor.