"Friendship"

I'm confused at how this simple word can be interpreted so many different ways. Friendship is trusting, loving, loyal, supportive, fun, caring and honest. There are no expiration dates. You don't just walk out when you have other things going on or when a better "friend" comes along. Friendship should be like marriage. You would do anything for your friends and be there forever. Why don't other people have this same philosophy?
I have one bff. We've been bff's forever. She knows practically everything about me and vice versa. I would never doubt that she would be there for me if I needed her and the same goes for her. If she pissed me off I could talk to her about it without hesitation and she would do the same. There is absolutely nothing big enough that could part our friendship. Nothing. As happy and grateful as I am to have my bff, I have to wonder if she is the only one out there.
Just when I thought I had a really close relationship with a friend, it ended. I don't know why or exactly when but it has. I was very butt sore over the whole thing but now that's turned to anger. I'm pissed that I allowed myself to get close to someone, shared personal things and brought our families so close. And for what? I want to tell this person how I feel but since I can't do it nicely I've chosen to express it here instead. She knows we aren't friends as much as I know we aren't friends and it's obviously not bothering her so why let it bother me?

I think I'll keep my bff and my family and to hell with everything else.