What is between a married man and a woman is spirituality. This is achieved by the two becoming one ~ Matthew 19:4 and Ephesians 5:31 "for the two shall become as one" In this way, through fleshly intercourse, they overcome the world, overcoming the flesh as they devour it through intimate contact; thus, arriving a greater entity which is not of the flesh but of the spirit. I say this as a Christian social psychologist. Many married couples who have experienced extra marital affairs often remark that it was either 'just' sex or it was a need to have sex for spiritual re-connection that the spouse was not giving. Such affairs are ungodly activities. And, this is why the Bible says, do not deny your spouse the experience of consummation, do not deny yourself this as a married man/woman. It is in this way, that a married couple, as one, overcomes the flesh and grows spiritually.
We can better understand consuming the flesh as overcoming it through spiritual engagement. Therefore, when we reflect on marriage as a consummation of flesh as in overcoming the flesh toward spiritual being, we realize that it was meant to be sacred. We can imagine that this is how Jesus viewed marriage. He said "In the beginning the Creator made them male and female; and said, "for this reason a man will leave his father and mother and be united to his wife and the two will become one flesh." Matthew 19: 4-6 And, also we can better understand when he told us to prepare for the marriage banquet. Jesus talked about marriage at the resurrection. He said, "At the Resurrection, people will neither marry nor be given in marriage; they will be like the angels in heaven." Matthew 22:30 This suggests to us that the flesh is overcome through marriage in this world so that our spiritual bodies can exist eternally in heaven with the Creator. We are thus asked through marriage to prepare for that day, prepare by overcoming the flesh here and now so that it will be totally consumed allowing for our spiritual bodies to resurrected.
When people go from partner to partner, they are not engaged in the deeper activity of overcoming the flesh but indulging in it. There is a difference.
*Read Ephesians 5 and 1 COR 7 to further understand marriage between a man and a woman ~ a spiritual oneness.