This case of the adulterous woman is very strange.
Which is why it is worth pondering in much greater detail, not throwing away. It is when we find something that does not seem to fit with our current understanding of God that we actually learn and grow, by seeing how we have to change our understanding of Him in order to accommodate all the facts. On the other hand, if we just throw away each passage that doesn't seem to fit, we'll never learn.
I agree that adultery is equivalent to idolatry. We cannot worship anyone but God. And the husband is dividing his wife's body, as if God is sharing his right to be worshiped with someone else. So will God allow us to worship anyone but him?
We, the Church, are the Bride of Christ. He is our Husband.
Nevertheless, He allows those of us within the Bride to marry each other here on earth. Is that adultery against Him?
No, because it is all within His Bride.
BUT we are not to be unequally yoked, ie to marry unbelievers, because that would be going to someone outside His authority.
The same applies to a husband allowing intimacy between two of his own wives - it's still within his "bride". Again, whether he SHOULD allow it, or whether it would be profitable, is a whole different matter. But it's not adultery.
And really, what makes me be against lesbian and homosexual sex is genesis. I see genesis 2: 20,21,22 as a model of sexual intercourse that God wants. The only honorable sexual relationship in the Bible is between man and woman.
Genesis does set the model of what God wants, I agree. However, lesbian and homosexual sex are very, very different things that should never be confused. Male homosexuality is repeatedly condemned in scripture, both old and new testaments, and given the death penalty in the Mosaic law. It is sin, unquestionably. Lesbian sex on the other hand is never mentioned at all in the Old Testament, ie never condemned in the Law (and as sin is disobedience to the law it is rather difficult to label it sin), and only possibly mentioned once in the New (Romans 1:26).
Two completely different issues, don't ever conflate them.
Christians who support lesbian sex do not approve of two women living together and adopting children. But the Bible also does not condemn two women forming a family, so what would your argument be that it would be wrong for two women to form a family without a man?
It is against the natural patriarchal order of the family established in Genesis and explained further later. God's pattern for a family is for it to be led by a man, with his wife (or wives) as his suitable helpers (help-meet). A family of two women has no head.
Having said this, you're right that two women forming a family is not condemned as sin. This means that if two women are forced into this through circumstances (e.g. widowhood, poverty etc), they do not sin. God's law is great like this - it leaves open options that are not God's ideal plan - not as loopholes to allow sin, but rather as allowance for the practical difficulties of life.
However it is not God's intended plan. Deliberately seeking this and deliberately rejecting God's order is another matter, as it is a deliberate choice to go against His Will.