My mom died when my oldest son was 14. One of the last things she told me was that my husband and i should have a "hobby" to do together. I was always running out to the gym, leaving my husband home. When he started cycling, I would go to the gym then. It was him forcing ME to get out there on his old mtb, pushing me up a small hill with the back of his hand, that embarrassed me into wanting to become a cyclist. We also do almost everything together and while, I have friends, I don't feel the need for separate vacations, etc.
Even if your adult kids come home, you still need common interests. I agree with Mr. Silver. Although mine have not returned to the nest, if they do, it's rent time!

Robyn