Legal Question in Family Law in Texas

If they were valifly married but weren't ever legally divorced (or had their marriage annulled or she's now deceased), then you're not now and never have been married to him. If their marriage ever does dissolve and you're still living together when it does, at that point, your marriage will legally take effect. Assuming they would have been divorced in Texas, which may it may not be the case, there's an online database of marriage and divorce records available from the State that you can download to your computer (I think it might also available at the library, maybe). You might try that.