Lost - you are feeling sad as life has changed for you, your little one has flown the nest!! My DS went last year, settled very quickly, enjoyed course, lots of friends, saw regularly as he not far away, but boy did I miss him and feel sad (but maybe a fraction less than I would have done if he was unhappy). Still have DD17 at home, which did help reduce sadness too.
I think it was worse after xmas, probably took me to summer term to really get used to it. I am missing him again this week, missing his presence after having him home for 3.5 months, but not sad like last year. (Although we seeing him again tomorrow eve to drop off forgotten stuff, he only an hour away and DH and I work half way there!)
I think the message is be kind to yourself, try and keep busy and be positive if they are settling in, enjoying course and staying in touch. And look forward to Christmas!
We dont have a busy social life, but I have been messaging various friends to go for walks or coffee on 2 days I don't work, and looking like I will keep busy till half term. Getting a date sorted to see my uni friends before xmas and DS said he wants to do xmas market with us again, so I think the term will fly.