For more than 30 years, Dr. David Nichols has piloted a plane or a helicopter across the Chesapeake Bay on his day off each week to provide medical care to this community of 500 that has no resident physician. He has tended to the islanders in an old building with a leaky roof and holes in the walls, no hot water and outdated equipment held together in some instances by duct tape. The island will celebrate the opening of a stunningly modern clinic with an official dedication on Aug. 29. The clinic is the realization of Nichols' dream and the culmination of a remarkable fundraising effort that spread far beyond the island. But the joy of this momentous occasion will be tempered greatly because as the island gains a new medical facility, it braces for an enormous loss. The island's family doctor is dying. The 62-year-old physician survived melanoma of the eye six years ago, but he learned in July that the cancer had spread to his liver. He said last week that, based on his diagnosis, he could have about four months to live.