Change is inevitable. Either you change or life around you changes. There are positive changes and sometimes people/things change for the worse; take a turn for the worse. It sounds like most of the changes you relate here are good ones and that you are happier and healthier because of it! Sometimes we find ourselves surprised by how we come out on the other side of change for the better. Yet, in other cases, what we predict would/should be "good changes" turns out not as good as we had hoped or predicted.
Change can be stressful. It definitely depends on the person, the circumstances and how drastic. Some people do seem to handle change better than others. Others do better with a certain amount of steadiness and change can FEEL unstable. How a person handles change at any given time may just depend on how stable they feel internally. Change can be going on around them, but inside they are a basically stable person and able to weather the changes better.
I don't mind change much at all if I feel it is good and needful change. What can bother me about change is when things change and there seems to be no good reason for it and it may even make things worse than they were before....so each person has to decide for themselves when to hold the line and keep things sort of the way they are, yet evolve and change internally as a person within that stability. Children tend to thrive on a certain amount of stability in their lives, yet they keep growing and of course as they grow they change. But even children are more resilient than we often give them credit for.
Cats and the elderly don't do so well with change. They can get through it alright, but they don't particularly LIKE it.
But in the context of addiction and co-dependency we have so many accounts of people who need to change (for the better), who are changing for the better even though it doesn't always "feel good" while in the midst of. Transition can feel threatening and scary to us sometimes because we are perhaps more than ever aware of how little control we may have. Letting go of that need to control is perhaps one of the hardest changes a person can make about their self....because being at least somewhat in control was like a security blanket of sorts.