How does the Trinitarian defend this argument from a JW? Upon discussing the relationship of Father and Son (the Trinity) with a Jehovah's Witness today; they disagreed (of course) with the understanding that the Trinity doctrine holds the Father and Son as One, but separate.

They quoted that the bible teaches that husband and wife become "one" and that this should be the way we view the relationship between Father and Son.

My question is; what is the biblical basis of explaining this and thus defending the Trinitarian doctrine against this interpretation?   I am specifically interested in the argument of the husband and wife "oneness" thing posed to me today by JW's as an apparent way to explain the oneness of God thus opposing the Trinitarian viewpoint.
According to Genesis, a husband and wife become one flesh (Genesis 2:24).  Since God is spirit (2 Corinthians 3:18), it is unclear how this Scripture fits their argument.

Furthermore, Scripture witnesses to the Divine Trinity in many other places.  For example:

Matthew 28:19  


  Go ye therefore, and teach all nations, baptizing them in the name of
  the Father, and of the Son, and of the Holy Ghost


2 Corinthians 13:14


  The grace of the Lord Jesus Christ, and the love of God, and the
  communion of the Holy Ghost, be with you all. Amen.


John 15:26  


  But when the Comforter is come, whom I will send unto you from the
  Father, even the Spirit of truth, which proceedeth from the Father, he
  shall testify of me


1 John 5:7  


  For there are three that bear record in heaven, the Father, the Word,
  and the Holy Ghost: and these three are one.