WL, welcome to the forum.
We ALL do things in our lives that are regretful. That does not mean we are bad people. Just people that made a bad decision.
Try to work on self forgiveness. We are truely our own worse enemy at times.
Your best friend has forgiven you, don't you deserve to let it go, into the past and learn and grow from the experience?
Here is a link that may help get you started. I have a great book, but it is on abuse, so it would not apply here. Check amazon and local book stores for self-kindness or compassion. It takes some practice, however with some will power it becomes easier faster than you think.
www.mindful.org/how-to-choose-self-compassion/Best of luck, keep posting we are here to support
Peace
Trina