I didn't grow up in a military family, but we were definitely "separated" from our extended family. My parents were born and raised in TX, but they ended up in PA by the time I was born. The rest of my extended family (grandparents, aunts, uncles, cousins, etc) all stayed in TX. I have a cousin I have never even met, but now we are back in touch via e-mail. So what's the point of my post, you ask?
Every year I send Christmas cards, and every year my list gets longer. At first it looks overwhelming when I write out the list of names, but then I look again and I am grateful for the military life I have lived for almost 10 years now. I send cards to my family (all over the US now) and cards to people I have befriended over the years. I may only talk to many of these people via e-mail, or once a year with a Christmas letter, but the fact that I have soooooo many friends is an amazing feeling.
Despite the uprooting and moving around on a relatively regular basis, I take my friends with me from one duty station to the next. The memories we shared are always in my heart. I have had the pleasure of meeting so many different people from so many different backgrounds - they each teach me something new and I cherish those people and friendships.
So, whether you have left your family for the first time (PCSed due to the military), or you have PCSed so many times you can no longer count them on your fingers and toes, just remember that each time you PCS you take things (friendships, memories, etc.) with you... you don't leave them behind :)