Am I entitled to half?

As long as your state recognizes common law marriage and you have satisfied the requirements for having one, in a divorce you are entitled to whatever assets you would have been entitled to had you been married in a formal marriage ceremony.

Oklahoma case law sets forth a five-part test to establish a common law marriage:

• An actual and mutual agreement between the spouses to be husband and wife;
• A permanent relationship;
• An exclusive relationship;
• The parties to the marriage must hold themselves out publicly as husband and wife, and;
• Cohabitation as man and wife (There is actually a split of authority on this particular standard).

The party asserting a common law marriage must prove all of these elements by clear and convincing evidence. This can be done with evidence such as joint income tax returns, joint financial accounts, jointly held assets, joint credit, medical records, insurance records, introductions and comments to third parties, hotel receipts, and any number of other sources. If clear and convincing evidence is missing as to any part of the above referenced test, the claim of a common law marriage will fail.

Additionally, Oklahoma is a community property state.  Therefore, if a valid common law marriage was proven, you would be entitled to 1/2 of all assets acquired during marriage unless your "spouse" could prove that they were separate property or were purchased with separate property funds.  However, he would have the burden of proof to show this; the court presumes all assets are community property.