It may suck for you, but tell your kid to not come home for a while. This is their time to shine and meet new people. When my parents dropped me off at college they were adamant that I do this (even knowing how much it sucked for them). It was sage advice.
Excellent advice.
Letting go may be the biggest gift you ever give your kid.
It says, "I trust you to make good decisions on your own in this next stage of your life."
When - and if - you miss the kid, sit down and WRITE (or type) a letter and mail it to him. It will be appreciated more than he will ever let on. Ask some intriguing questions about what he's studying. Stuff like "What has surprised you the most?" "Who's the most interesting person you've met so far?" "Who's your best professor and why do you think so?" "Has anything you've encountered made you angry yet?" Stuff like that. It will fill some of your gap time all the while being like sitting next to him and chatting at the dinner table.
When the nest is empty, you can fill the time and space with other worthy activities. Volunteer. Sponsor a local team or some cub scouts. Sign up for trivia night. Take trips. Go fishing, hiking, biking. Plan to meet up with the kid on his turf a couple of months from now for dinner and/or local sight-seeing or maybe a home FB or BB game.
At home, do dumb stuff that takes your mind off missing him. Make a video (maybe of pictures of your kid as he grew up). Sing karaoke. Make a video of you singing karaoke. Write and sing a song about him. Mention you have this and then tell your kid that you will blackmail him by sending it to his dorm. (don't...remember, this activity is supposed to be dumb, not cruel). Take up painting. Learn a new game, like backgammon if you don't already play it. Pick out an author and read every book s/he has ever written.
The idea is to change up your routine. Instead of those bi-weekly school events, take in a play. Go to the opera (everyone should do that once). Visit different churches (if you're a church-goer).
I know. I'm telling you to get so busy that you forget to grieve. But it's okay to grieve for what you've lost, even if it's a happy loss. Just don't make it your life's work.
P.S. Lucky, lucky kid whose parents will miss him. That's what I call winning the gene pool. Hats off to you, OP.