I was going to post this as a question about law, but anyway. So does anyone know if you can count as being married even without legally being married, in some states? Like if you are living with someone as a couple but you never really had any legal ceremony or signed any papers... can you in some states be considered as married? And if so in which ones?

You may be asking about common law marriage: A union of two people not formalized in the customary manner as prescribed by law but created by an agreement to marry followed by Cohabitation.

A fundamental question in marriage is whether the union is legally recognized. This question is important because marriage affects property ownership, rights of survivorship, spousal benefits, and other marital amenities. With so much at stake, marriage has become a matter regulated by law.

In the United States, the law of marriage is reserved to the states and thus governed by state law. All states place restrictions on marriage, such as age requirements and the prohibition of intrafamilial marriage. Further, most states recognize marriage only upon completion of specified procedures. A typical statute requires a witnessed ceremony solemnized by a lawfully authorized person, submission to blood tests, and fulfillment of license requirements. However, in some states, the marital union of a man and a woman can still be achieved in the most simple, time-honored ways.
Common law marriage legal definition of Common law marriage. Common law marriage synonyms by the Free Online Law Dictionary.

This articles says nine states and DC allow common law marriage:
Common Law Marriage