Man does not make the husband and wife one flesh. God does that. It is a statement of fact. For man, it is impossible to dissolve, because it is a divine and miraculous act of God, and man cannot change it even if he wants to. When two people are made one flesh, there is nothing, absolutely nothing in this world, no fact, nor circumstance, which dissolves the one flesh of two people so joined, but death itself.
Death is the only act which frees one from that divine bond.
This spiritual principle applies to both husband and wife. Neither is free in the Lord to marry again as long as the other lives. The circumstances of their relationship do not alter the fact that they are still one flesh, by a divine act. Now, let us consider some of the variations of that relationship, and find God's answer to them. Human reason and emotions often frustrate and confuse the divine order.