He never actually elopes with Mattie because if he did then it would not be as irrational of a decision. Because Ethan was married to Zeena and did not love her the way that he loved Mattie, he would almost work up the courage to do elope with Mattie and then something or someone would convince him or say something that would help him nullify his feelings and begin to feel remorseful for even beginning to think that way. The relationship between him and Mattie almost forced him to abandon his wife and do the unmoral thing to do and run away and start a new life. Had it not been for some little reminders that were always presented to Ethan whether it be someone he knew complimenting him because he had so much patience with his sick wife or the financial aspect of eloping and basically running away with nothing but the clothes on his