As we grow up, we get more mature and change as people. Sometimes as we grow up and change, we miss who we used to be. We also miss who other people used to be.
Some of those changes are good, but some changes people go through aren't so good. Minor things that will make you think maybe they, or even yourself, were better before they changed.
Don't get too worked up about how much someone has changed, but instead focus on how it has helped them, and you, for the better. Embrace the changes. Get to know them again. Get to know yourself again.
There are times I look back and think why was I like that, or was I really that naive? All of those things that happened before helped shape who I am as a person and even though I wish I could go back and change the past or fix whatever it may be, all of that made me who I am today and helped me to be a better person.
If you don't like who you are, or something you do, change that habit. Learn how to do that specific thing better or more in control or rational.
If someone changes and you think they changed for the worse and is going to be toxic, or are toxic now, leave that friendship or relationship. Don't stay to make other people happy.