Hep c for long term monogamous couples is not considered to be an STD by the Center for disease control. In fact the CDC does not suggest the use of barrier protection for such couples. There have been many people here on this forum where one partner has hepatitis C and the other does not.
Is he seeing a doctor to obtain treatment for hepatitis C? With the new meds available over the last several years hepatitis C is almost 100% curable.
His treatment could be as simple as one pill a day for a few hours eight weeks and he could be cured.
Before the new medicines were approved over the last several years I had hepatitis C for 37 years. I treated with the old medicines that were less effective on three separate occasions but none of them worked. Three years ago I treated with one of the new medicines and I am now cured of hepatitis C.
He should speak with his doctor about the new medicines like Harvoni, Epclusa, or Mavyret. Then get treated and cured of hep c.
My best to you both