Should I go for it and tell my boss?

Hi I would like some opinions here. I work in a company with such a great benefits but the think is I have a bad boss. She is so untrustworthy the fact that she stab me on the back twice. Now, I have this close co-worker who would stand up for me and nice to me (at least this is what she said, yes it did happen once or twice infront of me that she is standing up for me.) well, what happened is that she got promoted by my boss and out of the blue she stabbed me on the back. I felt so hurt and owh buoy I felt so mad and could not believe it. She actually asked my boss to tell me that I hope I was not mad at her. Well, I think she did not dare to come talk to me because she knew she did me wrong. Now, I have some information that I haven't shared with my boss about her because in the first place I thought I could trust her. To be honest this gal has done anything wrong in my boss's eyes and my boss actually told me that this gal would stand up for me and etc. The funny thing is that my boss would do things outside the work place with this gal. But my boss did not know what this gal had done such as peeking on someone else's pay stub even though I already told her not too but she did not stop doing it. So, I feel like I gotta say something to my boss because all this time I kept my mouth shut about her but this gal stabbed me in the back and now I become the bad guy in front of my boss's eyes. I also felt like everybody going against me in this company. I am a straight forward person if I see something that is wrong I would say it to their face and a lot of my friends said that this is one of the cause why these people did not like me. so what do you guys think? do you guys have any suggestions?