infected with what? there are many types of stds you did not mention what type that he has. if it is herpes then it is still possible to transmit herpes to your mouth throat or genitals even if he does not have an active outbreak. this will be the risk you will take. your partner should also be thoroughly tested for other stds. consider using condoms and safe sexual practices until he get the okay from all of his tests.
is it safe to perform oral sex on my infected partner if there are no symptoms present?