Okay, let's review. You dated him for just a few months. You haven't spoken to him in months. You knew he was leaving but you didn't bother to see or even call him. You never loved him.
Yes, I can see how you would be devastated by his departure.
How do you get over it? Have a sandwich and watch some Modern Family reruns. You'll be as good as new by tonight.
No, I get it. Sort of. Now that he's gone, you appreciate and miss him more, especially since he was the first guy you dated, and you wish you had taken time to see him before he split. Unfortunately, you didn't, and there's not a thing you can do about it now except take to heart this very important life lesson: enjoy people you care about while you can--friends, boyfriends, family members, parents--because one day they will be gone.
Thanks for the question.