I know it is hard but you will adjust. I have had 2 leave for uni and this year my only dd is going. The second she told me she had had written confirmation via track that she her place had been confirmed, ie even before she had her a level results, I felt my eyes pricking (though I hid it of course).
What helps for me is thinking of it, as badbadkitten said, as though they are going off to boarding school, though mine have never done that. They still essentially live at home, they are just away for the term.
The first term is the hardest. I know I felt very sad for a week or two, then you start to adjust. It is always so exciting to see them again. The pain when they leave after Christmas is less than the pain in September, and by Easter, it is quite easy to let them go as the summer term is often short.
Remember you can still talk to them via Skype etc. I actually talked to my reclusive ds1 more via Skype than I sometimes did when he was home!
And maybe try to give yourself a treat or a distraction? We unexpectedly adopted a stray kitten a couple of weeks after ds2 started uni. Maybe go away for a weekend, or just enjoy having less housework, or eating food your child has never liked. There are positives to be found if you look for them.