at a loss

I know I shouldn't be so sad but I am at a loss. For 26 years my life completely revolved around my kids. I worked and then would spend every possible moment with them and didn't actually take the time or effort to cultivate other friendships because I wanted to make sure that I took as little time away from them as I could because I have worked two jobs 7 days a week for many years so anytime I was off I spent with my kids. Now my kids are all grown. My 23 year old just moved out on her own with her boyfriend and my 25 and 18 year old are still at home but I know its just a matter of time. I know it is supposed to be this way yet I can't help but I can't help but feel sad and really struggling with the idea of my kids not being there everyday.