Married gay couples are one flesh as well, especially from a legal perspective.  Catholic hospitals did not respect this and exiled partners, which is why the marriage movement started.  BTW, Jesus was quoting Babylonian Rabbis who attributed the man-woman passage to Moses.  Moses did not say it.  You are essentially appealing to authority rather than reason.  If reason wins, that is the side Jesus is on.  If you don't understand that, take up knitting.