Good afternoon and thank you for posting on the Final Fantasy XIV Technical Support Forums.

Do you recall anything updating/changing on your PC that coincides with this?

Do you receive any kind of error message when the game closes?

First I'd suggest trying a clean boot. Simply open the task manager and select the 'Start up' tab. Disable everything here and restart the PC. This will make sure that no background processes are interfering with the game.

Also make sure to close all other unnecessary programs while playing the game, especially overlays (Geforce Experience, Discord Overlay, etc.).

We hope we can be of assistance in helping you enjoy the exciting world of Final Fantasy XIV!