Chances are, he is missing you too.
It's a big jump, but he is not gone forever.
He will be back at Christmas with the biggest bag of laundry known to man!
Try and take up a small hobby.
Do you draw, paint, knit?
Give the house a good tidy.
Volunteer somewhere, if you have time.
Agree a time to call him for a chat every week or so. Show an interest, even if you can't help,with his homework anymore...
And send him an "SOS" parcel every month. Some non-perishable things. Pasta, cans of beans, you know what he likes.
Also, more expensive things like sticky plasters, painkillers etc that he may not buy for himself.
And a tesco/asda whatever is nearest to him gift card.
Be pleased that you have done such a good job bringing him up.