Those are complicated questions but most of what you asked, the answer is yes.
What I don't agree in is how people change for the worse. It is weird when I meet people that are so dependent on their surroundings whether it be their family or friends. They get so hurt over things that I think i would never feel anger towards. Like if your boy gets a girlfriend, you'll be mad that he changed. I am like, who cares....let that dude learn his own way. But the main thing though why people change is really is really all personal. It could effect others but by the end of it, a person has to do what a person has to do. You as an individual just have to change when other changes come your direction. It's the people that stay stagnant that really can be a problem. People develop and the world changes. You can't just sit their and expect all things to be catered to you.
Anyways...it's not as complicated as it seems. It really is just life and you won't even notice when you cross over to that other side.