be in (something) for the long haul
To be dedicated to doing something for a long period of time. This phrase usually describes one's commitment to someone or something. Jill knows that obtaining a PhD is going to be tough, but she said she's in it for the long haul.
be in something for the long ˈhaul
be willing to continue doing a task until it is finished: Trust me when I say we’re in it for the long haul.