Smallville: Promise

Clark decides to tell Lana his secret on the day of her wedding to Lex which she discovers on her own; Dr. Langston knows something about Lana's baby and Lex kills him accidentally; and, Lionel Luthor threatens to kill Clark if Lana, who plans to run off to Clark, doesn't fulfill her vows to his son. She ends up going through with the wedding to save Clark who is left behind bewildered and crushed.