Do I have to file for divorce or annulment?

If your spouse was already legally married to someone else at the time you got married in 2011, then your 2011 marriage is void as a matter of law and you cannot seek a divorce. However, you may have assets, debts, or child-related matters that need addressed and that would need done where you (or he) reside (or where the children reside). Under these circumstances, many people will choose to proceed with an annulment, so the record is clear (for taxes, credit, property ownership, retirement accounts, etc.). You may seek an annulment in Nevada (since you were married here), where you reside, or where he resides. In making the decision on where to proceed, you should determine whether or not your spouse will cooperate, how you will prove he was still married if he won't cooperate, and convenience factors including time and money.