For a couples night I highly recommend doing the Asticou Azalea Garden in Northeast Harbor, then heading to the harbor to look for seashells and end the night with a picnic on the beach.
Topographic map, Mt. Desert Island & Acadia National Park, Hancock County, Maine. [TIFF]. Yarmouth, Me. : DeLorme, 1986.. Retrieved from https://maps.princeton.edu/catalog/princeton-6t053h81q