I think we all need time alone. I'm having a problem with this too since my husband retired. My youngest son still lives at home too. Between the two of them, I am rarely alone and it doesn't feel good at all.
The best thing I can do is get totally absorbed in whatever I'm doing at the time. I know you can't do that when you are taking care of children though.
I sure hope you can figure out a way to have a little time to yourself. I think it's really important. I'd better work on it too.