Every relationship we have, though, may end due to any number of reasons. That some old friends are uncomfortable with the way we've grown is just one among many. It's painful to lose a friend in that fashion.
That they fail to be able to adjust to us growing and that they selfishly insist we not change shows that they're just not good company to keep at this time. Anybody who can't be happy for us in our relationships isn't capable of being a close, supportive friend. If they refuse to remain friends, it's their choice.
And they may be back some day. I've had people I've walked away from in the past pop up a few years later and apologize for their behavior.