Empty nest syndrome

My two daughters are 7 and 9 years old and since few months, I am freaking out (and have a lot of anxiety) when I think about them leaving our nest. I know it is not for tomorrow and I have a good 10 more years with them but I hate this idea.
I love my life today with them at this age, and I am terrified about losing this (which I will because undeniably they will grow up and live their own lives). I really enjoy spending time with them and doing many activities.
I think I am having anxiety about this subject because my life then will be so much different than my life today and I cannot imagine it or imagine how it can be. So I cannot project myself into the future. I am also afraid of being alone, by myself, lost and not know what to do of my life/time/days.
I don’t know what I could do to stop having anxiety about this subject.
Thank you so much for your help!