I remember when I first went through my divorce, my son saw his dad very little. When he did go to be with his dad, I felt like my entire being was living in another home, eating meals with another family, and hugging someone else before bed. I was heartbroken and completely paralyzed to any other thoughts or actions until my son was back home "where he belonged". It took words of wisdom from a very close and honest friend who told me that missing him was okay. Paralyzing myself and the deep depression and anxiety were not. The hardest thing I did was to take the step into normality and life while my son was with his dad. It took practice to learn that life still goes on and that I should use this time away wisely. Most people call it a "break" but in reality it shouldn't be a break from yourself, just your normal responsibilities. In fact, when I took time to really focus on what I wanted to do that I normally couldn't do, it was a sense of freedom and fulfillment that gave me more energy for when my son returned. It was like taking the car to the mechanic and getting maintenance done so that the car (me) would be in better working condition for many days ahead.
While he is gone, he is growing and bonding with his dad and I am growing and bonding with myself.