I feel your pain. When my oldest moved away to college, she got terribly homesick and for the first two weeks she called us every few hours, crying, begging to come home. She was mainly exhausted, not being able to sleep in a noisy dorm. After she got used to it, there was no problem. But of course it was SO hard to tell her she had to stay. We knew she would love it once she felt more comfortable there. The other daughter went three years later, but to the same school, so they lived together, which made me feel a little better, but it was still tough to let them go.
Right now I'm sobbing inside for a friend whose triplets (2 girls, 1 boy) just graduated and will all go away to school in the fall. Her house will be so empty and quiet! She's been a stay-at-home mom since they were born, so will really miss them terribly.