Today I did not cry

Why is it that when one of my older two children leaves to go back to their home I get so sad? I want them to be independent of us, but there is a part of me that wants them both to be here all the time. My daughter left today to go back to her life after spending her vacation with us and a couple of extra days at home. We went shopping, talked, and just were together as a family. The only thing that could have been better would have been if the older son had been here too. I was a bit down this morning when I woke up and I think it was because I knew she would be leaving. Heading back to her adorable apartment and her nursing job. Now the house seems quieter and I'm sad. It has taken me years to accept them growing up and leaving home. Years to not cry EVERY time they do leave and say goodbye to me. I still do cry sometimes and they know that it is just part of their crazy mom. Today I did not cry...but I thought about it.