Rather than just apologizing, have you told/shown your friend how helpful she's been? Are there any suggestions she's made that might be a good idea that you might be able to do now (like the finally telling your parents) that you weren't able to do before?

What did your parents do with the telling? You probably should see a therapist it sounds like? Can you ask your parents to see/talk to someone and see if they can help with ideas how to show your friend you appreciate her and miss her and would like her to be friends again.