My husband and I recently found out that he was never divorced from his first wife; what does that do to our marriage?

Unfortunately, I am not certain.  Common law marriage is not recognized in Florida but it appears that under Florida code Section 741.211, there may be hope.  Specifically, the statute states "nothing in this section shall affect any marriage, which though otherwise defective, was entered into by the party asserting such marriage in good faith and in substantial compliance with this chapter."

The problem is both you and your husband knew of a pending matter but didn't check to ensure that the divorce was finalized.

Further, this is going to be a serious matter because under Florida code section 826.01, being married and marrying someone else is a felony in the third degree UNLESS he believes he is legally eligible to remarry or his wife has voluntarily deserted him and remained absent for three years continuously.  At this point, it comes full circle and your husband may be able to have the previous marriage terminated by virtue of abandonment. 

Your marriage is void.  As long as your husband does not have a final divorce decree he is still legally married to his "first" wife.  What he needs to do now is to file and finalize a divorce.  At such time you can legally be married.  Until then you are not husband and wife.

As long as he entered your "marriage" in good faith (ie he believed that he was divorced), there should be no criminal consequences to this.

As for the divorce itself, in FL, one of the following facts must have occurred for a final judgment to be granted:  (a) irretrievable breakdown of the marriage; or (b) mental incapacity of one of the spouses.