Was I wrong to say anything? How can I fix this?

Last week, one of my friends (lets call her G) said something really insanely bitchy about my other friend (let's call her J behind her back), and one of guy friends (I'll refer to him as D) told J. I had already been mad at G for saying rude things to me, and when I found out about this, I was pretty mad, but not to her face. Late that night I had a three way Skype chat with J and D. They were both really fed up with G and at that point, I was too, so I told them about every single thing rude and offensive G has ever said about J. She had said things like, J's a dumb blonde, she only acts stupid for attention, she's not that good at clarinet, and she said she's better at J at dance. All of those are COMPLETE opposite of the truth. J was pretty mad, and I told G to apologize to her, about the first thing (that started this all). While G was apologizing, J told her should couldn't accept because she had been saying crap about her. G denied ever saying anything like that and blamed it on me. Fortunately, I knew that it was true and so did J. Now G won't talk to me, J or D, but she's insanely pissed at me and D for telling.G thinks I'm a ***** and a liar, and I made her look bad, but nobody believes her that she didn't really say it. Now I've lost a best friend, but managed to keep a very close one... I want to make things better, but I don't know what to do. Was I wrong to tell them what G said?