Hey there, Julia. If you're reading this, I want you to know that you're loved by a lot of people and that you're a great friend. Sure, what happened with your former friend was awful, but I'm happy that you wanted to make things right with her. God wants us to forgive others, no matter how hard. It's way better than holding a grudge against someone anyday. Grudge holding is bad for not only you and everyone around you, but it's also bad for your health: physical, emotional, mental, etc. I know that it didn't end well, but in the end, what you did showed that you were the bigger person.
What I recommend is reading the Bible everyday. Make time for God. We should always put him first, others second, and ourselves last. There's a lot of verses in the Bible that talk about stuff like forgiveness, so those can really help you out. You'll find those mostly in the New Testament.