Hi Lana. While I suspect it is somewhat different for everyone, here's my story. I felt an enormous sense of loss for about a month until my son and I established a routine of contact. I sat in his room and cried a couple times. Once we got that contact established, it was much easier. I guess I realized he wasn't disappearing, he was moving on to the next chapter in his life. And I moved on in mine by taking college courses, changing jobs, and ultimately moving across the country for a job at a university.
I think it's a bit like grief; you go through stages. Also, while my son and I were very close, he was never the "whole" of my life. So, look at it as an opportunity. You have spent years teaching your sons how to be in this world; sit back and delight in them becoming fully independent.
Pat