How do I deal with the inevitable? Kids growing up? (Dad to his daughters)

Small history before I get into it. I was adopted at the old age of 8, no 'true blood' family to experience. Also me and my adopted family are kind of not that close. I grew up without that strong sense of family. Holidays were a chore for me more than a thing I wanted to do, etc. You get the idea, I just didn't have that family bond like my wife does with hers.

Fast forward to meeting my wife, falling in love, getting married, having kids, buying a house, the whole nine yards and I'm happy with it. I'm a lucky man for sure!

I have two amazing daughters that I've become extremely (maybe even unhealthy) attached to. They're my only blood after all... well that I'm aware of! They're my princesses, my girls. It's been, is, and always will be a privilege and joy being their father.

The issue for me now is they're growing, I'm slowly losing the title of being their favorite person in the world (well and their mom too, but I secretly think I'm the fave 😜 j/k). And I know I have to let go, but every time I think of it, it makes me feel so cold inside. I don't know how to explain it, but it's hard. I truly feel like I'm losing a part of me which I know isn't the case and isn't a healthy way of thinking of my girls. I just love spending time with them, and making them laugh, and slowly they're starting to get more interests in other things and I support it, but deep down I'm sad about it.

Does it get easier? How does someone deal with that, or is this something I need to see a professional on?