This sounds tough. It sounds like classic "empty nest" syndrome. I'm sure he is finding it very hard too. It's a long distance and I expect you're worried about losing touch, and perhaps feeling lonely? You also say "this life is shite... I don't want to be here". This is super worrying, can you talk to someone about this and get some help? It sounds like you're depressed. It feels like more is going on than just your son moving away- I suspect there is a root cause you need to tackle. Maybe you're putting a lot of reliance and your mental wellbeing on your son?
More directly related to your son, can you put in some structure so that you both see each other? For example, arrange for you to visit him in the summer. And ask if he can come to yours for Xmas? It's going to be hard on him too, but it is normal for adult children to move away and see parents less. Especially during uni. Perhaps getting some dates in the diary will help, and not leaving it all on him to visit you.
One thing you want to avoid is making him feel guilty- this is a great opportunity for him, and will open many doors, you don't want to hold him back. My friend's DC didn't leave home or go to uni because they didn't want to leave their mum. They're now working in a minimum wage bar job. The area she lives has terrible employment prospects. Maybe try to think about what's best for your son in the long term? Make sure he doesn't feel responsible for you or your happiness, you have control of this and you can do it! You can get through this. Change and adjustment is hard, but it's doable. Have strength.
It will also help if you have your own life and social circle. Do you have a job you can throw your time into or some hobbies? Find some other passion or interest to fill your time, so you can start enjoying life and having a purpose.