Some ex best friend help?

Okay, so I have a problem. Let me begin the story. Me and Lisa were the best of friends ever since elementary school.(Currently, we're starting 8th grade) Then in 6th grade we had a bad quarrel and I did/said really mean and hurtful things. She got her revenge in 7th grade by making me jealous of her new so called "friends", etc, I really want to apologize to her, I feel soo guilty and it's turning into a form of depression. I just want her friendship back and let her now I'm deeply sorry. How do I word it? Thank you very much all who answer!