A down-on-his-luck soap-opera actor took his own life this week after he was forced to put his beloved dog to sleep under pressure from his New York City condo, friends said. Nick Santino euthanized his dog, Rocco, on Tuesday, on Santino's 47th birthday. That night, his guilt over the gut-wrenching decision became too much to bear. "Today [Tuesday], I betrayed my best friend and put down my best friend," he wrote in a suicide note, according to close friend Stuart Sarnoff. "Rocco trusted me, and I failed him. He didn't deserve this." Santino -- a struggling actor whose TV credits...