If you are legally married according to your federal laws but separated, then you can still apply for the common law marriage. However, this will depend on your agreement as the common marriage has a limited number of jurisdiction and they are not fully recognized as marriage. You can talk to your attorney for advice.
Are you married to each other? Or to other people? If you are married to each other you are married till you are divorced, separated or not separated means you are legally apart but legally married if you break the separation you are still legally married.