This comment repeats most of what Opus17 has already stated in his answer. Is there some part of it that you don't understand? Have you followed the 3 parts in Opus17's answer that are required for you to be common law married?
If you have followed them and consider yourself common law married, then you must file either married filing jointly or married filing separately. It is almost always better to file jointly than separately. Texas is a community property state which makes filing a married filing separately tax return somewhat complicated. You are not required to submit the document for informal marriage to the county clerk to be considered common law married.
If you have not followed the 3 parts to be common law married, then you each must file single or if eligible, one of you could file as head of household and the other as single.
Once you are married (common law or otherwise), you must adhere to all the laws for married couples including community property laws. You must get a legal divorce if you choose to no longer be married.
