Is it normal???

My son just left today for boot camp in San Antonio. We have always been so very close since it is just the two of us and needless to say, we are very close. Seems like I just can't stop the tears now that I am back home. Everything is a reminder of him. It's only been a couple of hours, but I feel as if my heart has been ripped out. Is it normal to be in a "grieving" state of mind? How long do the tears last...I can't seem to hold them in and I've always considered myself a strong woman and not a crier, but I sure am now!! How do I overcome these feelings? I held them in until my son left and I supported him all the way.