I regret it everyday that my bestfriend doesn't know that I'm the one who outed her to her mom and ruined her life
What did you do to your best friend exactly?
I outed her to her mom because of a fight between us.
It's understandable that you'd feel regret over ruining another's life. You should come clean and tell her this.
No I'm not going to out myself. Why should I tell her that when she's a bit of a slut and she does not seem to care about me.
If the regret you feel bothers you enough you will talk to your friend. Sometimes our conscience keeps after us to come clean.