If you're not in a good state right now, then perhaps now is a time to reflect on the source of your feelings (which you seem to be doing anyway) and find a healthy outlet to heal those feelings, possibly speaking with a T, journaling, or another activity that allows you to blow off steam and clear your mind of what's troubling you. Once you organize your thoughts and take the time to consider how you want to address the person who has actually hurt you, then maybe you should with reasonable and honest intentions.

I think once you're able to do this, you should address the friend you un-friended and explain where you were coming from. You're not a bad person, and it is Facebook - it doesn't necessarily define or dictate how you handle friendships IRL. Apologize to them and ask if you can leave can be FB friends again. I'm sure if they understood how you were feeling at the time, they would take this into consideration. You can even do this sooner and maybe ask them how you should speak with the person who hurt you.