That provision of the law, INA 212(a)(1)(A)(iv) is a provision that the visa applicant has been determined in accordance with the regulations of the Secretary of Health and Human Services to be a drug abuser or drug addict and that makes them excludable from the United States.
The Form DSL-851A is not a form that you fill out, it is just the document that lists what I just stated above. Your fiance has been denied a visa because he has been found to be a drug abuser or drug addict.
Here is a link to the form that he would need to use to apply for a waiver (forgiveness):
If he is denied the waiver, then he would have to wait 3 years and apply again and they will test to see if he is clean. I am truly sorry for the bad news.
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