Who should my best friend be? Long time friend who moved or newer friend who's here to stay?

okay, last year one of my good friends gwen moved away, leaving her best friend Isabel by herself. My best friend, aymi, and I didn't really talk to her much then. but now this past year we have become friends, but during the year I missed out hanging with aymi by myself. And a few months ago Isabel said something like aymi was her best friend, even though aymi and I still consider each other best friends.... and now aymi is moving. I don't know what to do... i still want to be best friends with aymi but I don't want to hurt Izabel's feelings. I've been spending lots of time with isabel lately but I still miss my bff. Me and aymi have been friends since the second grade.... I'm so confused!!!!!