Not Goodbye, Adieu

I have never broken up with anyone before.
I married at age 19, to the first person I had ever kissed. Luckily for me, we still, after almost 15 years, like each other and more importantly still like kissing each other.
I dated guys before, but without an official break up. I usually phased them out, or they started phasing me out. This is how, we usually stopped dating.
This is the same with females in my life. We usually stopped calling each other or stopped hanging out and the plans to get together soon, halted completely.
Recently though, my best friend for the last couple of years, and I mutually broke up.
Our relationship had changed. I don't think it was intentional, I think it just happened. It happened at about the same time, with each of us spreading out in different directions. The strong pull we once had, was no longer there.
She e-mailed me and brought it up first.
I read what she had to say, and she was right. We were no longer "us", the "us" we used to be.
Our relationship began with one of us saving the other through means of being a "sounding board" for the other. This bonded us.
As the years went by, the obstacles were different. I didn't need to ask her for her opinion and she didn't need to ask me to figure out her puzzle either. And suddenly, very suddenly we no longer had things to talk about.
Thus the break up.
As I said before I have never broken up with someone before. I never had the courage to say, it's time, it's over.
Although there was never a sexual-anything with her, I still feel a deep sadness.
It was time. We both agreed it was the right thing to do. Moving on was the only thing to do.
But I still feel like a sliver of my heart was taken out. And that piece feels awfully hollow now without her.
I have this image or maybe a hope that we will be the kind of friends that enter and exit each other's life over and over again.
Maybe years from now we'll bump into each other and the conversation will be and as if the years hadn't passed us by, but rather had been put on "pause".
Perhaps this will happen, maybe it won't.
At any rate, I wish her luck. I wish her the best, and I wish her Adieu.