I promise it will get better. You are not over reacting. I started the same type of thread as you back in 2011. Has it really been that long ago?!! My oldest had been in college for 2 years when my twins both went off to college. We moved all 3 into college the same weekend. It was horrible to come home to an empty house. My husband and I literally stood in the kitchen held each other and cried. We weren't ready for our new reality. It was a very difficult transition for me. It took a long time for me to get used to it. I felt like I hadn't had enough time with them. It was too soon for them to be gone.
You will get used to your "new reality". It will just take time. They all did come home to visit at various times and we went to them, but it isn't the same and it will never be the same. You will adjust and then the new life you lead will be your normal.
Mine have all graduated from college and are back home again
I know it won't last and my babies are gone, but they are wonderful adults now. And that's my new reality.
Good luck to you...you will survive!