I feel exactly the same.
DS1 chose the army over uni and left in July 14. I used to hide in the bathroom to cry many, many weeks after he left. He didn't come home for the first 7 weeks, then it was just a weekend. He came home again 7 weeks after that.
When we had to take him to his Phase 2 training, after he'd been home 2 weeks, I cried for 2 hours coming home in the car. Then we saw a convoy of trucks carrying the vehicles he was going to driving and I cried the rest of the way home.
DS2 went to uni in Sept, he's doing nursing so he only gets 7 weeks holiday and no reading weeks! He, also, has lectures 9-5 atm so has only been home once, last weekend. I miss him terribly.
We are incredibly close, always have been. I'm disabled and have had major surgery in May. He's looked after me since he finished his exams, he took me places, made me meals, painted my nails. He wouldn't leave me although I said he could. It hit me like a tonne of bricks when he left. I cried almost all the way home. I couldn't eat. I cried that night when DS1 went back to camp and I hadn't done that in months and months.
I am so proud that our DC have both acheived, so far, what they set out to do, but no one warns you of how hard the leaving bit is. I did say to DH maybe if they'd caused us more trouble and hadn't have been so lovely we'd have been happier to see the back of them! 