This appears to be an old thread, but I'll post to it anyway.
The hardest time for me in letting go of my son - he's an only child, and was alone with me from the time he was born - was when he turned 11. He and I had moved to another province just after his fifth birthday, and we wound up living almost 1000 miles away from his father. His dad never really did bother wanting to see him, and Stephen didn't hear from him again until he was 11. That summer his dad called and asked if Stephen could come and visit him...so we made the arrangements and my son flew back home to stay with his dad for the summer. That had to be the longest 2 months of my life, I think. I did manage to keep busy and entertained myself, it was tough. Actually, I do recall the first week being rather enjoyable; had the place to myself and it was quiet! But by the end of the week...I really began to miss him. And it made me realize that some day, he would be gone for good.
Stephen wound up visiting his dad every summer for the next 5 years, and each year got a little bit easier. It also helped me in a sense, because he's now 24 and has been away at college - about a 6-hr drive away, and neither of us has a car - for the past 2-1/2 years. He has no plans to move back home, as this city isn't really geared toward the film industry, which is what he is pursuing...so I know that I won't be seeing him very often from now on. However, the things that have helped me through this are: the telephone and the Internet (he and I keep in touch every few days), and the fact that I know he's on a journey to fulfill his dream.