It would be hard for me to consider someone who did that a "best friend," even in retrospect. You must have placed more value on your friendship than she did, otherwise she would have had more respect for your feelings. Same goes for your boyfriend.
If, by "forgive" you mean go back to the way things were before, I wouldn't do that any sooner than I would crawl back in a hole with a snake that just bit me. At the same time I wouldn't let it become a nagging sore either. My reaction would be to kill them with class. Deal with them in a business-like way and raise yourself to a higher level. There are plenty of guys and girls out there with enough loyalty to deserve your trust.
In the long run, I suspect you will realize you didn't lose much with either of them. Take the high road and leave them in the dust.