I went through my daughter's graduation last Sunday, and she went home to Ohio with my family on Monday morning to stay with them for a while. She does call every day, but it's not the same. Then, she starts college in August.
Trust me when I say that I know exactly how you feel! The house is eerily quiet (my 16 year old son is still here, but he's very quiet unless his friends are here) and empty.
The thing I'm trying to remember is that if we've raised them to be self sufficient adults who are productive members of society, we've done our job. It's not easy for me at all- I wish she was 3 years old again. I really miss her.