That really hits home with me as well.  When I was born, my mother made friends with another woman in the hospital whose son was born the day after me.  They stayed in contact and he and I grew up friends.  He was practically my universe (at least as far as my universe extended to include other people; I had a rich fantasy life!), and we used to play pirates or go frog wallowing or other stereotypically "boyish" activities together as often as we could.  He moved away, too far to visit, when I was about 7 or 8.  I've had no contact with him since.  It was very painful for me, I cried a lot and was miserable for some time.
Since then I've had other super-close friendships, including going through periods of time where I had acquaintances but only one friend I truly had any interest in playing with.  Absolutely none of them were ended by me, but by the other person- usually when they moved, switched schools, or some such.

Until now, it hadn't really occurred to me that this isn't necessarily a "normal" pattern of friendship.