Her concurrence with the judgement of Lawrence v. Texas was only on the basis that Texas singled out homosexual sex specifically. In her view, states could ban blow jobs and anal sex for everybody, but not allow it for straight couples and ban it for gays.

I must say the logic has a certain appeal to it. If sex truly is a private matter between two people then cohabiting with multiple partners as if they were spouses should be legally protected too under the same logic. But if we say equal protection is what matters and you can't specifically single out gays, then that problem goes away.

As it is, Lawrence has opened up a fair bit of uncertainty what the Supreme Court will do to Lawrence and de facto bigamy laws (enacted in really only a minority of states) if and when they review a case on appeal. (Most states do not recognize informal arrangements as potentially bigamous.)