I was a bit ahead of your position this year - ds1 graduated and got a job hundreds of miles from where we live, ds2 is half way through his degree (we are in Scotland - degrees are 4 years), and ds3 (my precious last-born) left school and went off to university.
I will be honest - I was dreading it - dh works away a lot (his job changed and he moved to a different arm of his company, and instead of having an office half an hour from us, in Glasgow, his office is now on the Edgeware Road in London), and I didn't think I would cope with being alone.
But I was wrong. Yes, I was upset when ds1 left home - it was a wrench knowing that he really doesn't live here any more - but that is outweighed by the pride in knowing he is doing well in his job, and is really enjoying it. And whilst the house is very quiet, with no teenage boys in it, that is actually quite nice - the bathroom stays clean, the fridge isn't getting raided several times daily, we are only running the washing machine once or twice a week, and the ironing pile is almost non-existent, compared to the Everest that used to build up each week!
And they do come home - to raid the fridge, do their laundry, and see their friends. Ds3 has just texted me to say he is on the train home - less than 10 minutes before his train departed - there's nothing like giving your mum a bit of notice, is there??!
Luckily I have made casserole and mash for tea, and there will be enough for three, but we have been decorating the spare room and all the stuff from there has been dumped in his room because it's the nearest - he will have to sleep in his brother's room.
You will cope - it is a new phase of life - I know that, four years from now, ds3 will graduate and leave home, and then all three will be visiting U.S., not coming 'home' - but I am trying to look forward to it as an opportunity to do something new - new hobbies, more of my existing ones, maybe an OU degree, and spending more time with dh, who will be retiring about then.
I know how you feel, though - hugs!