Tuned, an app designed for couples, is now available on iOS. The app comes from the NPE Team within Facebook. Though Tuned is billed as a private app for couples, users should be aware that anything sent through Tuned could be sent to third parties for targeted advertising, per Facebook's data use policies.
https://www.notebookcheck.net/Facebook-releases-Tuned-an-app-that-gives-couples-a-private-space-to-message-each-other.460250.0.html