> what does it mean for gays (or anyone) to not be married in the US?
Do gay couples get to be legal couples?
Do straight couples have any legal rights if they're not married?
Every State is different, and then there is the US gov.
There's a player here who does Law in another life and can correct some of what I say.
I have a gal, call her "R". We are married. Therefore I can add R to the group health insurance at my work, and my Pension can be set-up to cover R between my death and her passing. I can apply the Health and Pension to my children in addition or instead.
If these plans were open to "anybody", I could sell health insurance to the highest bidder. Probably somebody very ill. It would skew the insurance payouts very badly. Instead the plan covers only active employees (presumably healthy enough to work) and a finite set of Close Family, who may be well or sick, but on-average will not be very sick.
R automatically shares all my property. Major property requires both of us to sign-off on a buy or sell. Upon my death, without specific instruction, she owns all my property. And if I instruct that all my property go to someone else, a widow can claim a share anyway and the court will decide. Marriage is a much stronger position than "Palimony".
R and I automatically have custody of "our" children. This is far less certain without a Marriage. Unmarried, if disputed, mother has custody until a court decrees otherwise.
This exposes the real though obsolete reason we have marriage. Formerly males owned all property and females bore their children. Property passes from father to son. But.... is that brat MY son? The only way to know is to be sure no other male impregnates my wife. Then all her issue must be mine, and should inherit my property. Therefore I select a virgin (or at least not knocked-up), stand in front of the whole town, and vow to each other. If she is faithful (most of the town will help by letting me know if she is unfaithful), then her children will inherit my property.
Of course that does not stand up today. Property is not male-only any more. Cars and hourly motels make a sneak-off real easy. DNA can establish biological fatherhood; non-blood children are presumed to have rights in the family which raises them (especially if Adopted). We live so long our children are well established before they inherit our stuff. And the medical system keeps us going until there is nothing left to inherit.
There is well-established tradition of Common Law Marriage. However legally it is a much weaker position than a state-recognized Marriage. The legal assumption is "just friends" until you go to considerable effort to prove long-standing relationship equivalent to a marriage.
In this state, I do not believe a "friend" without your Living Will may make major medical decisions for you, next-of-kin can, and spouse has priority. In practice, a Wife may have priority over a friend who has your Living Will... that may not be law, but it may take considerable time to establish who pulls your plug.
A few years back, my state-employee benefits office extended "spouse" to "domestic partner", including same-sex; but there was no legal binding partnership recognition. At the time, I felt this was good social policy but poor fiscal policy. If I were single, I'd find a sick guy willing to buy a piece of my health insurance and call him "partner". No proof of partnership needed, and I could change partners nearly at will. Last year the state established a formal Domestic Partner license: you go to the town clerk and fill a form very much like a marriage license, vow before a pastor or judge and get it signed, and have it registered at the state record office. There are subtle details which make it less than a Marriage, but it does formally establish a Partnership which can not be dissolved casually (I suppose eventually some of these couples will flow through Divorce Court). And I believe it presumes joint ownership of propery and joint custody of minor children with right of survivorship (unless otherwise contracted).
You can not take Life Insurance on a stranger. You need a formal relationship. Family, sure. Business Partner, yes: if one dies, the other may wish to buy-out the widow's share. A friend, even a friend who lives in my house for a long time, generally would not be able to get Life Insurance against my death. With Domestic Partnership status, this should be possible.