This is a problem. It's not healthy to allow yourself to be defined by another person. This is why it's very important for women, especially, to find a way to fill the time when their children are grown.
As an example, my mother homeschooled us starting when I was in Grade 4. She continued homeschooling and online schooling until my youngest brother started Grade 10. By this time she had been a SAHM for 25 years. But when Bro4 started at the local high school, she started taking cello lessons (she is a pianist, organist, and singer already), joined a cello ensemble, and started taking language classes at the local uni (she is fluent in French, with a B.A. in French and an M.A. in political science; she started taking German classes). Today she and my father teach a course in scientific writing for people who are ESL speakers, and she is the current president of her church women's group. She was proactive in developing her own interests, which I think is fantastic.
I do sometimes wonder if this is why some women start "taking over" when they become GMs, even if it's against the AC's wishes.