There is no separate Facebook Dating app or Facebook Dating site; the feature is integrated into the Facebook mobile app. If you become Facebook friends with some after matching with them on Facebook Dating, you can still see their dating profile.

Why did my Facebook Dating app disappeared?

If Facebook Dating is not showing up, you probably need to update the Facebook mobile app to the most recent version. Enable Facebook app notifications. If you have turned off app notifications, make sure you make an exception for Facebook or turn notifications back on.