Dating my best friends ex?

Me and my best friend have been friends for about 10 years. I had my eye on this girl and since i was not able to drive to see her my best friend starts to date her. This lasts for about 8 months and they broke it off. It has been a while since i talked to her and when i did start talking to her my friend got mad at me even though he was the one that broke it off. This girl has been on my mind for the past 4 years and now that I am able to see her my friend gets mad at me even if I talk to her. My friend he does not get mad at me long if i do something to piss him off but I don't want to push it too far. When my friend and the chick were dating my friend would talk to her on the phone for hours when i was there and he knew that I would have wanted to be with that girl. With what has been said do you think that my friend would stop talking to me if I was to date this girl. She is still on my mind and I don't know if she would be worth loosing my friendship. At the same time I never had too much luck with chicks while my friend has no problem. If anyone could give any advice it would be greatly appreciated.