Be it their looks, habits, lifestyle, friends...whatever!
Well, unfortunately for those who think you cannot change, it's impossible. You will change. Your likes in music will change. One day you'll love something and the next day you will be sick of it. Don't worry, you are changing. As you grow older, you will find yourself liking less physical activities... Why? Circumstantial situation - your body aches and things get difficult and you decide you cannot run a marathon like you could when you were 20. This means that you might love running now, but in 40 years you'll hate to even walk.
In terms of relationships, usually if you are comfortable enough, you will change to adapt to that relationship. If you love someone a lot, there are certain things you will do because you are not alone anymore. It's not me, it's we. Maybe if you like something with a passion, she cannot ask you to drop it because she wants you to do that. She could try but will you let her?
On the other hand, some of your things such as taking a vacation whenever I feel like it for however long is a different story. You cannot simply disappear without word. You have to talk with your significant other and tell her stuff. Remember, it's not just you anymore. She'll change too! If you live together, she'll pick up a few habits that you never thought would happen that will make your lives easier. It happens. She's changing too...
The first sign of change, believe it or not, is the fact that you learned to love her. Your views on her are different, therefore it's the beginning the way she's making you change. And remember, if there are things that are absolute (like you cannot change the fact that you hate meat or something) make sure she knows that before she tries.
Don't worry, people's personalities are dynamic, not static. The person you love in the beginning will not be the person you love at the end of your life.