Sort of the wrong section but I'll gladly still respond.
You didn't really state how old they were, but I'm guessing 18 - 23? Somewhere between there? That's at least the most common age of when the children move out.
If you miss them, and wish for them to stay / drop by regularly, let them know, tell them you want them to come over for dinner every once in a while, have a small family get-together, or ask if you can come by and visit them once their place is decorated and done. Being supportive is also good, support them in their decision, try and help them out, and let them know you're there. The worst thing to do is start arguing because you don't want them to move, forcing them to stay is a bad decision and will most likely result in them wanting to lose a bit of contact, harsh but true.
If it's their first time moving out, it's quite common for them to drop back at least once before fully moving out and standing on their own two feet. But let them know that you're there and willing to help out with anything if they need something.
Something that can help you out some, is starting a hobby if you have the time, not sure if you got a job or not, but work, distract your mind a bit.
Hope I could help some?
Also welcome to ChristanChat!