Most Helpful Girl
No, I don't think you should forgive her.
Not only did she cheat... she did so with your best friend.
Clearly, she has no sort of boundaries.
You don't need someone like that in your life.
You may love her.
But you don't always need what you love especially if it's harmful to you.
Move on with your life.
You have the rest of your life in front of you.
Although it may not seem like it,
you'll meet other girls eventually.
Many of which would not betray you in that way.