The short answer is probably not. To show a common law marriage, there needs to be enough facts to convince a judge that both of you lived and behaved as spouses "typically" do. Agreeing to be on a health insurance plan and sporadic cohabitation alone will most likely not count. Many other factors come into play, such as did you introduce yourselves as husband and wife, did you get wedding rings, did you take his name, did you have children that took his name, did you file married filing jointly tax returns, do you have jointly titled property (autos, real estate, etc.), do you have shared bank accounts, credit accounts, lines of credit, etc., are there witnesses who would come forward and testify that they thought you were married? The list can go on and on, but the key point is whether you both held yourselves out publicly as being married. Note, that your engagement and potential marriage to another is evidence that you don't think you're common-law married. As a practical matter, it would be up to your "ex" to bring the petition for dissolution, if you didn't think there was a common law marriage. Don't worry about any bigamy charges because you honestly believe you're not married. If you are really concerned, you could file a creative petition for declaration that no common law marriage exists, but unless you think your "ex" is going to bring a common law marriage action, I wouldn't worry about it.
I would agree with Jeff, except that I would add that you need to be careful about talking about this situation around the insurance company. Some companies are starting to cry foul as to the representation that was made... don't go there with them.
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