This app was mentioned in 10 comments, with an average of 1.30 upvotes
Do you mean like a shared Google Calendar or shared lists in Wunderlist? The "Between" app also is designed specifically for couples:
https://play.google.com/store/apps/details?id=kr.co.vcnc.android.couple
Between is an app created exclusively for couples to send to each other. I can't vouch for it, but sounds like it would fit your use case:
https://play.google.com/store/apps/details?id=kr.co.vcnc.android.couple&hl=en_US
Utiliza la app between.
https://play.google.com/store/apps/details?id=kr.co.vcnc.android.couple&hl=es (android)
https://itunes.apple.com/us/app/between-the-app-couples-love/id458035189?mt=8 (ios)
My girlfriend introduced me to Between and it is a decent app. We probably use the image gallery, private messaging and countdown clocks the most.
Website (includes mobile and desktop download links): https://between.us/?lang=en
iOS link: https://itunes.apple.com/us/app/between-private-couples-app/id458035189?mt=8
Android link: https://play.google.com/store/apps/details?id=kr.co.vcnc.android.couple&hl=en
Using Between since a long time https://play.google.com/store/apps/details?id=kr.co.vcnc.android.couple
I saw this app in a k-drama and planned to use it if I ever get a partner.
https://play.google.com/store/apps/details?id=kr.co.vcnc.android.couple