You have to bite the bullet one more year. The filing status you use on your 2016 return is based on your marital status as of 12/31/2016. If you were still legally married as of that date, you have to file MFJ or MFS. The fact that he's on disability is irrelevant.
If you and your ex-husband did not live together at any time during the last 6 months of 2016, and if you're paying more than half the cost of providing a home for yourself and a dependent child, you could file HOH.
But you won't be able to file Single until next year, when you do your 2017 return (unless you remarry during the year).
**Answers are correct to the best of my ability but do not constitute tax or legal advice.
