the rest have given really sensible good advice.
I know when i took my eldest daughter to start university in Wales (200miles away), I
sobbed non stop for the first 100 miles home i think!!!
I knew perfectly well
she was ok - her neighbours in the halls of residenced has already made friends with her and they were off to a disco at the students union ... it was that great big hole in my life without her!
You do need to think about YOU now and as has been said - you adapted your life to fit them in all these years and now you adapt again.
Give time to
your interests - I was already doing my fine art degree as a mature student when my daughter left - that really helped. It was so absorbing. She was also a handy base for painting in the Welsh mountains! - she was at Bangor uni so Snowdonia was right near - wonderful!