Would you be mad at the girl in this situation?

I've been dating this guy for 4 months and some stuff happened. One of my best friends (S) has this other friend (B) who goes to another school just a couple miles away from ours, so they hang out every chance they get. Especially now that school's out. I was at the mall last Saturday with my boyfriend and a few other friends. S and B were there too. And at one point we all came together. Now B is way prettier than any girl at our school... I have to admit that. But my boyfriend didn't even seem to notice her. But he disappeared sometime while we were there. Late last night I was talking to a guy friend (E) and he told me everything that happened. E is my boyfriend's BEST friend. And I know for a fact that he likes B too, so he probably told me everything, so HE could get B.. Which I don't care, as long as I know about MY boyfriend. So after he left me Saturday he went downstairs to see E. S and B had already been with E. So in short, my boyfriend flirted with her and even went as far as saying he'd kiss her on the spot. But she had heard from S that he had a girlfriend (me), so she wouldn't talk to him. But he told her he didn't have a girlfriend! But she was still wary. So he asked for her number, he gave it to her, and later that night he called. They talked, she got pissed off because she confirmed that I was his girlfriend, and he again denied it! So finally she started to believe him.. But then the next day they talked again.. Still not sure what about. And then the next day he asked her to a movie with E and S. And then E and my boyfriend 3-way'd with B last night and she was pissed AGAIN that she knew he had a girlfriend and he finally admit to it and said he just said that because he knew she wouldn't talk to him if she knew about us. She started ignoring him, so he asked her what she wanted him to do about it and she said "Break up with her. That's the only way." and he said it's "harder said then done" since we dated for so long. And she said something like "So you do like her?" and he said "No, it was a mistake asking me out.. He wasn't thinking." So she said break it off and get back to her when the deed's done and hung up on the both of them.. So I asked my boyfriend about it all this morning and he acted like he just got caught stealing and said "We'll talk about it later on.. I'm busy." What do you think of the situation? Do you think E made it sound worse just so there would be too much drama for E and B to be together? And would you be mad at B? I'm most definitely mad at at my boyfriend though. If I find out it's all true, I will never be speaking to him again.