Okay, ya know what? If that's really all there is to it then you need to fucking grow a pair of testicles and tell your buddy that you like this chick and are going to see what happens with her unless he flat out tells you he's got issues with it. If he can't similarly grow a set and tell you he doesn't want you to pursue her then that's his own fault. No need to be some kind of mamby pamby sissyboy about his feelings if he can't tell you when you ask him straight up.

*edit*

On the other hand, if you are sure that it's gonna bother him and you value his friendship then you should consider which is more important to you. At some point YOU have to make the decision because surprise surprise, this is YOUR life and not ours.