NEW YORK (Reuters) – It's official: R&B diva Rihanna says she is back together with Chris Brown, who is still on probation for assaulting her in 2009, saying "It's different now." "I decided it was more important for me to be happy," Rihanna told Rolling Stone magazine in an interview published on Wednesday on its website. "I wasn't going to let anybody's opinion get in the way of that. Even if it's a mistake, it's my mistake," she said of her renewed romance with singer Brown, 23, that has prompted consternation from fans and celebrity media because of their history. …