The life lesson is that you will change. You will grow. You will develop. You will do things you swore you would never do,change your mindset, give up things you treasure, let people go that you cherish. You will change and that is absolutely definitely positively okay. You are human and the way that we think and reason constantly changes! You do not owe anyone your stagnancy. Anyone who can't get on board with the fact that you've upgraded your thinking or your mindset needs to hit the exit sign real quick.
People like to throw the phrase 'you've changed' in a bid to hamper your self esteem and keep you shackled to their stagnant regressive mentality and it's up to you to resist that. Life happens to the best of us and along with it comes change, growth and self development. Yes you have changed over the years and there is absolutely nothing wrong with that. Embrace your journey, its yours and no one elses.