John Gill Commentary Mark 10:8

"and the two shall become one flesh: so that they are no more two, but one flesh." — Mark 10:8 (ASV)

And the two shall be one flesh
This is the remaining part of the citation out of (Genesis 2:24) ; (See Gill on Matthew 19:5);

so then they are no more two; but one flesh ;
as Adam and Eve were both by creation and marriage: and so two persons, a man and woman, being lawfully married together, become one flesh, or "one body", as the Arabic and Persic versions render the phrase; and therefore the wife is to be loved by the husband as his own body, and from whom there should be no separation, until death, but in case of adultery; (See Gill on Matthew 19:6).