As a teenager, Joe Kemp struggled with drug addiction and the urge to commit suicide. But Kemp, 43, now an assistant vice president of public relations for Northwell Health and a former managing editor at The New York Post, found salvation — which, on this National Suicide Prevention Week, he hopes to pass along to others. It should have been my last glance at the outside world, but I took little notice of the cloudless sky or the plush green trees in my parents’ backyard.