Yeah it gets better. 
Took me a while, maybe 6 months. I missed my daughter TERRIBLY when she went to uni, and I felt bereft, and sad, and really quite low.... But by the end of her second semester there (so say, by around March/April,) I had got used to it, and so had her dad (my DH.)
This was 7 years ago, and she has never lived at home since... She now lives with her boyfriend in another town 25 miles away, and we see her 2 or 3 times a month. (She visits us once a month and we visit her twice a month.)
We have a wonderful relationship, and love each other to bits, and we speak on the internet (twitter/facebook etc) 2 or 3 times a week..... But she has moved on with her life, she is a fully fledged adult, she has a long term relationship with someone she now lives with, she has a busy, successful, professional career, and a busy social life, and lots of friends, and I could not be more happy for her.
You will feel the same @daffodillament
Maybe not by tomorrow, or even by next month, or even by Christmas, but it will get better soon, and you will learn to love the freedom, the lack of responsibilities, not being 'mum's taxi' anymore, having to do a lot less household chores and cooking, and the quiet and tidy house. 
Also agree with the posters saying don't visit your son at uni!!!
I mean, if he ASKS you to - that's a different matter, but don't just turn up uninvited and unexpected.