How do I file after common law married and filing joint taxes last year, now separated this year

Last year 2016, me and my now ex filed taxes as married jointly. We weren't married in a court but found out if we filed taxes that way, we would be considered common-law married afterwards. We ended our relationship April 2016 and we've been living separately since then.That was the only time where we filed married. We also have one child together. And he also didn't work at all in 2016 but I did. How should we each file this year? This happened in Texas. And we never followed suit with an official marriage decree or anything of the sort.