"To fly the coop" means to leave a place or situation, often when someone wants to become independent or escape from restrictions or crowdedness. Full definition
It's just the two of us as all the kids flew the coop years ago and are scattered all over the US, but I still make a full Thanksgiving spread! (thegunnysack.com)
The unwillingly divorced or dumped are not known to be so happy (that's half of them versus the ones who flew the coop for new loves or lives, although divorced women with children do tend to become happier than many married women with children). (psychologytoday.com)
Still, as in the past, it was well over a year before the 2001 Inc 500 companies that were started at home finally flew the coop, often with handful of employees in tow. (inc.com)