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I do not understand your question. Did someone begin to answer your question, and not complete it?
Unless both your boyfriend and his ex considered themselves married, lived as a married couple, and held themselves out to be married, they were not common law married. They would have had to file taxes together, use the same last name, tell people they were husband and wife----things like that. It does not matter if they lived together because that alone does not make them married.
If, however, he did consider himself married to her, then he has to get a divorce. Common law marriages, as I described them, are as valid as the ones where you get married by a minister or justice of the peace.