If a people are filing taxes together and then being common law married can one partner sue and file for divorce?

Idaho no longer has common law marriages.

In party, that would have to be divided, otherwise, they don't need a divorce and each could go their own way.

Filing a joint tax return claiming to be married is only a single fact that might be considered tax fraud or it might be considered evidence of a common law marriage. Which of those is correct depends on much more information that you haven't provided. Generally, a common law marriage requires that both parties intended to be married and conducted their lives consistent with that intent. However, there are no simple rules to say whether or not there is a common law marriage and nobody will ever know if there is one until a judge hears all the facts and makes a ruling one way or another. If there is a common law marriage, it can only be ended by a judicial divorce. The threats to "take everything he has" is probably little more than the angry ravings of an ignorant person who doesn't know or understand the law and can be safely ignored unless and until she actually files for divorce.

Georgia recognizes the existence of all common law marriages that were entered into before a certain date but does not recognize them after that date. It is a bright line cut off rule. If they are married by the common law, then they can get divorced.

Filing Taxes does not necessarily make them married. If he does not want to be married, it is unlikely that they are. Tell her to file it.

There is no such thing in Wisconsin as common law marriage. If they aren't legally married, they cannot file taxes together or get divorced.

If they aren't married they can't file joint taxes. No common law marriage in CA.

There is no common law marriage in Arizona. Unless they have a marriage license and have had a ceremony, it is not a valid marriage. He should consider amending his taxes however and filing separately, in order to avoid potential tax fraud issues.