If all of this happened in Ohio, a bigamous marriage is void ab initio.
Quote Quoting Snyder v Snyder
This Court recognizes that it is well established that a bigamous marriage is void ab initio and of no legal purpose. One who is already married has no capacity to enter into another marriage contract, either ceremonial or common law. Johnson v. Wolford (1927), 117 Ohio St. 136 cited by Darling v. Darling (1975), 44 Ohio App.2d 5.
Who told you "that he must obtain a divorce from her before we can be married"?

If he's not clear on the status of his marriage, he can certainly consider seeking a formal judgment of divorce or annulment. But if he's sure that the rule set forth above applies, the bigamous marriage is void.