>I just don't want to be alienated from my best friend.

Is Vanessa your best friend? Why would she be alienated from you?

As for your breaking up, it's as they say: there are plenty girls out there, imaginary or not, so do not despair. Basically you outgrew each other, and did not fit together. I think you should look forward for the new kind of relationship that fits you better now. Probably your best times are ahead of you, you just have to keep dreaming ('^-^)