Things are changing:
When a person leaves, I now say goodbye, without bitterness.
I used to take it very personally. Of course, this does not apply to all people. But the exceptions I can count on the fingers of one hand.
When I want to leave, I now say goodbye, without sadness. (And the number of people who'd try to stop me I can count on the fingers of one hand.)
Comes with practice - years and years of practice. But this is a good place to be.