"First of all, in some passages God seems to tacitly sanction rape. In the Old Testament Moses encourages his men to use captured virgins for their own sexual pleasure, i.e. to rape them. After urging his men to kill the male captives and female captive who are not virgins he says: "But all the young girls who have not known man by lying with him, keep alive for yourselves (Num. 31: 18)." God then explicitly rewards Moses by urging him to distribute the spoils. He does not rebuke Moses or his men (Num. 31: 25-27). "Here's what God says about this:
Mark 10:4-5
They said, "Moses permitted a man to write a certificate of divorce and send her away." "It was because your hearts were hard that Moses wrote you this law," Jesus replied.
So God tells them directly, that Moses and the other prophets gave commands that were, not from God, but from men. He gives the reason for that here also. It was, because of the hardness of their hearts.
God's moral code is objective and the same code can be uncovered by men. It is because they are in the image and likeness of God. The objectivity of the code is found in the nature of man and of God, because both are of the same likeness.
If God were morally absolute as you contend then he would have not allowed Moses (his representative) to give such laws. God did not rebuke Moses for advocating sin, so God remains morally relative, just as he was when he winked on polygamy etc. Your argument actually serves to further prove my point.