When I first heard the word cleave, my initial thought was “What a strange word?”, What kind of language is this? It sounds so preachy!
But over the years I have come to understand it simply means this:
– as wife, I am now the most important person in my husbands life, after God, no longer his mother, father or family (he must leave them emotionally and cling to me tightly and I to him)
– I am one with him, closer than any one else must ever be (he must be faithful to me and I to him)
What a beautiful word : CLEAVE
Genesis 2:24 KJV
 Therefore shall a man leave his father and his mother, and shall cleave unto his wife: and they shall be one flesh.
Genesis 2:24 NIV
 That is why a man leaves his father and mother and is united to his wife, and they become one flesh.