I took an APTC for insurance in Jan and Feb of '18. My son was married in June and not claimed as a dependent in '18. Do I still count him when preparing my form 8962?

Was he covered on the1095-A?

Yes. When I applied for subsidized insurance he was a full time high school student living at home.  This was true ther two months i accepted the APTC

No, if you did not claim him on your return because he was not an eligible dependent, you will not count him.