The marital union of a husband and wife is everlasting:
After giving birth to her third child, Leah stated that she will call him Levi, as now her husband will be with her. This idea is based on the Zohar who states that married couples remain together forever in the upper worlds. Now, since Yaakov had a number of wives, it was unclear which wife is his true Zivug, and will merit to be with him in the future. Leah felt that after baring three children for Yaakov, she is the one destined to merit to be with him.
 Ohr Hachaim Hakadosh Parshas Vayeitzei [shelishi]
 Mishpatim 102