I found a great and so cute app called Between. It's a private app for couple. Here, you and your partner connected and every information is privately shared between the both of you.
Official website here
First page that you can set your anniversary date and picture. Memory box is a place where you want to save your precious memories.
An album for you :)
You can chat between you guys. No one else here except the both of you. They have a cute smiley and a cute background too.
Memos sharing :)
Since it's private, you may want to save the passcode. It's more secure in that way. You can set different tone for notification and chat received. And of course the tone is cute too.
Owh how I love a cute and kawaii thing!
Wanna try? Go here and it's all free. Plus, this app also available for Android user too.