This is an incredibly sweet idea. "Open when you need to know how much I love you; open when you don't feel beautiful; open when you need a laugh; open when you miss me; open when you're mad at me; open when you need a date night, etc.
365 reasons why I love you jar. Both have their own jar and write once a day one thing they love about the other. On their anniversary/birthday/valentine's day/christmas/whatever the occasion, open the jar and read what the other person wrote