Clinging Mom afraid to release a college aged child

Can you help me "let go" of my son who is heading off to study at university? I'm worried about the challenges he'll be facing on his own – challenges to his faith and his moral values, not to mention the practical challenges of living on his own for the first time. We've always been a close-knit family, and sometimes the thought of seeing him go is almost too much for me. In fact, I've been lying awake nights thinking about this. How can I deal with this transition?