Since you have noticed this at least at the age of 16, it appears to be a disorder of long standing and since only area surrounding one eye is affected, it almost certainly has to do with some skin problem, such as increased capillary supply to that region such as port wine stain
Usually black eye is noticed in case of iron deficiency anemia
, but then it should be seen on both sides and not restricted to one side.
I think it could have been present since birth.
I suggest you consult an expert dermatologist
and seek his opinion.