It sounds like TDCJ (I assume you refer to Texas Department of Criminal Justice) treats you as his spouse for their purposes. However, it doesn't necessarily mean that you are recognized as spouses for any other purpose. You may wish to consult an attorney in your area to clarify your situation. Most of the time, among other things, you must "represent yourself as married to the public", which it does not sound like you've done (prior to the incarceration or now.) Simply cohabitating for a certain period of time, even in Texas, does not create a common law marriage.
If the TDCJ is the only institution that recognizes you as "married", I'm inclined to think that you are likely not but there aren't enough facts here to determine that.
Please do speak to an attorney before you file a joint tax return, though. Please. Because if you file a joint tax return (which does require his signature), and you weren't considered legally married under Texas law before then you may very well find that filing in this manner is the thing that crystalizes this marriage, then necessitating a divorce. It doesn't sound like you want to be married (since you indicate you're no longer in contact.)
I suspect you're just the person TDJC wants to call "wife" and not legally married but definitely seek legal counsel. This type of thing is something your local legal aid may actually be able to assist with (though they typically don't handle family law matters.)
