Yeah, I think it's important to remember that people change and move on, regardless of what you've done. I was a military wife for many years and friends would come and go like the changing wind. Either we were moving or they were moving. That was something I had to come to terms with, and it had nothing to do with alcohol, whatsoever.
That said, I lost a couple of good friends due to me isolating myself when I was drinking. And, it is what it is. It's sad, but as Dee said, all I could do was take care of myself and move on. If you take a step back, you will see that people come into your life for a reason and it's not always easy to understand.