This post really resonates with me. I often dream about people from my past, and there are some recurring characters, including those that I wouldn't have thought would have had such an impact on me at the time. I have always wondered why these particular people seem to have made such an unexpected impact on my dream life when they seem relatively small in my waking life, but I hadn't thought of them in terms of the larger context of who I was at the time. I had a falling out with my best friend a couple years ago that was never repaired despite my efforts, and it's really gotten under my skin. She is one of the more expected characters who frequently makes it into my dreams. One aspect I hadn't considered until I had a revelation about it the other night is that the reason that our parting hurts so much and affects me so deeply is that after 14 years, she knew me better than anyone, even my own family. If someone who knew every nook and cranny within me decided that I wasn't worth having in her life, that must mean there's something terribly wrong with me. On the other hand, I have to consider my place in her life and what those times meant to her, and what I might remind her of--the aspects I'm not in control of. Reading this is making me consider that aspect, which is a little easier to swallow.
Anyway, this comment has already gone on forever, but all I mean to get at is that reading this has added an extra dimension to my own understanding of my dreams and ultimately, my motivations. So, thank you.
As much as it hurts, and especially when the reasons remain unknown, people often leave our lives for their own progress in life and ours. It's a contract. Your friend may return, when both of you are ready.