My fianc has 3 painful black spots on the roof of his mouth, his dad died of oral cancer how worried should i be?

Very: Get him to the oral surgeon for an evaluation right away. Best to be sure.

I am concerned : Given the history and the description of the issue I am concerned enough to recommend that he sees an oral surgeon and have a biopsy done if necessary. Good luck.

See an oral surgeon: These black spots are symptomatic. See an oral surgeon or an ENT asap. A thorough examination of the mouth, face and neck will be needed. Your doctor may recommend a biopsy procedure. Good luck.