My boyfriend started having a slight discharge from his penis so we got checked all test were negative except I was treated for bacterial vagnosis and he was treated for ngu but the discharge never stopped he has no pain no anything just discharge... what could it be?

The list is endless. If he's still experiencing discharge after medication, he should return to the doctor.

He needs to go back, the doctor missed something, or his treatment did not completely cure the issue.

You should not have sex, till checked with doctor and proper treated.