What if we both like the same guy?

I asked this but im asking again..I had this best friend who liked this guy. I started liking him and one day he just asked me if I liked him and I said yes. He told me that he liked me too. I never told my friend cause she’d be hurt..Even though I hurt her anyway.. This guy told my friend that her and him are friends and thats all they will ever be. I figured once she knew that they are just friends, that it would be ok if I went out with him.. I did go out with him and I currently am, but my friend ‘didn’t know’. She thought we were joking when we said it, but I didnt know she thought that.. Another friend of mine told her, and the same day, she called me and totally SPAZZED! She was saying things like how could I do that to her? and that the worst part was, was figuring it out from a friend. And I told her that I thought she knew cause we told her… Me and her are somewhat friends, but were never going to be close again, and I don’t really want to be. Do you think what I did was wrong? Or am I just the ‘B’ word? Like I don’t understand why I shouldn’t of went for it.. I knew just as well as her that he wasn’t going to ask her out.. !! :(