I totally get it. I miss my daughter everyday and she is 36. She was home for 3 months when their house was being built. We had a good time together, but she missed being in her own home and I missed having my space. It is a bittersweet moment when they do what they are supposed to do and grow-up and become independent.
Think about things you have always wanted to do but could not because you were raising kids. It takes time, but you will find your passion.