Soap opera star Billy Miller, a three-time Daytime Emmy winner known for his roles on “The Young and the Restless” and “General Hospital,” died Friday. He was 43. Miller’s agent told The Post on Sunday that he struggled with manic depression. His death, in Austin, Texas, was first reported by soap opera journalist Michael Fairman. Miller was just two days shy of turning 44. The Post also reached out to The Belmont, one of several Los Angeles bars Miller co-owned. Born on Sept. 17, 1979, in Tulsa, Oklahoma, Miller grew up in Grand Prairie, Texas. He was in and out...