How you filed your taxes is only one factor a court might consider in determining whether or not you had a common law marriage. It is not sufficient on its own.
There are 3 (really 4) elements that must be satisfied to establish a common-law marriage in Texas. Generally, you must have both agreed to be married. Next, you would have had to live together (cohabitated) as husband and wife. Third, you must have held yourselves out to the public as husband and wife. Not to be forgotten is the fourth requirement, you must have done all three of these things at the same time. See Tex. Fam. Code §4.401(a)(2).
Generally, the state will also not recognize a marriage that is specifically prohibited or that is against public policy. Examples would include incest or underage marriages. See Tex. Fam. Code §§6.201-6.206.
Did you both intend to be married? Did you live together as a married couple would? Did you introduce each other at social events as husband and wife? Did you wear wedding rings? Did friends think you were married or consider the two of you to be married? Filing your taxes as married is certainly evidence of your agreement and intent to be married, but that is only one factor the court considers.