Nick Carter is “completely heartbroken” after losing his sister, Bobbie Jean. The Backstreet Boys member broke his silence on her sudden passing while referencing the deaths of his other siblings, Aaron and Leslie, and saying he’ll never fully process the loss his family has experienced, RadarOnline.com has learned. As this outlet reported, Bobbie Jean died on December 23 at 41. She was found unresponsive in her Tampa, FL bathroom. Nick celebrated the holidays with his wife and children before publicly paying homage to Bobbie Jean’s passing. On Thursday, theI Want It That Way singer, 43, share…