If the virus is not detectable in your blood which if you have a blood test at four weeks of treatment is generally the case your risk of transmission is very low. Not detectable does not Necessarily mean that the virus is completely gone. It only means that the virus is below detectable levels for the test. But it does mean that you have very few to no virus particles remaining in your bloodstream which is why the risk of transmission is very low.
Hep c is not generally considered to be a sexually transmitted virus. While there is a risk for those who have multiple sex partners or for those who engage in rough sexual practices or in the presence of HIV, people who are in long term monogamous relationships are not suggested by the CDC they have a need to use barrier protection ie condoms as the risk for such couples is very low to almost non existent.
Hep c is a blood born virus transmitted primarily by sharing IV drug paraphernalia between drug users or having a blood transfusion prior to 1992 When testing for the hepatitis C virus was developed and the blood supply secured.
Hepatitis C virus is not spread by sharing eating utensils, breastfeeding, hugging, kissing, holding hands, coughing, or sneezing. It is also not spread through food or water.
Just to add once your are more than 12 weeks post treatment and the virus remains not detectable this is considered cured. You will always test positive for hepatitis c antibodies but you will test negative for the virus. Once cured you no longer have the virus so you cannot transmit hep c to anyone. You cannot transmit a virus you do not have.
Best of luck