When I got married, my life changed. When I got pregnant, my life changed again. And later, people kept telling me not to wish my son were walking solo, because "your life will change." (It changed for the better -- I was able to walk upright again!)
Change isn't a bad thing, just different.
We change a tire, and that makes the car move much better. We don't worry that it will "change things." We expect it to, hope it will!
Yes, of course any major life event will change your life. Doesn't make it bad.
My "baby" is now 16, and yes, my life has never been the same. But now that he is gearing up to go to college f/t, I'm feeling sad to see him go. It seems a lifetime (well, technically, it IS his lifetime!) ago that he was a baby. But it's hard to imagine my life without him, too.
I remember, before we had him (we were married 10.5 years before he was born), hearing other couples refer to their married life before kids as "when we were single" -- and thought it was funny. Now I understand. It's a similar transition. Wonderful, eagerly embraced, but life-changing, sure.