FALMOUTH — Everything finally seemed back on track. David was home for a short visit and looked happy, calm. He had a job, a girlfriend, a plan. His father, Kevin McCarthy, came home from work that Thursday and smiled to see his son take his dog, Kima, named for the drug-fighting detective on “The Wire,” out for a long walk. When David came back, father and son settled in to watch their Patriots play the Jets on “Thursday Night Football.” David gave his father grief about the TV being too small: “Come on, Dad, get with the 21st century.” Near halftime, David got up and said he was going to watch part of the game at a friend’s place. When David returned an hour later, they watched the end of the game together.