"For this reason a man will leave his father and mother and be united to his wife, and the two will become one flesh."This verse is a quote of Genesis 2:24. The context in Genesis is the creation of man and woman. The woman was taken from the man's flesh, and it is "for this reason," as the verse says, that a man leaves his parents and is united with his wife. It is a one flesh relationship.
This relationship is meant to be permanent. As it goes in our wedding ceremonies, "...till death do us part..." That is the way God intended it.