okay so  imagine your OTP and every year on their anniversary, person A gives person B a necklace with a little heart locket on it.

 Inside it is a picture of person A or a picture of the two of them. A does this so B can "always hold them close to their heart". One year A dies, and it's almost their anniversary. B goes out and gets another locket, putting a picture of the two of them in it. B then puts the locket on A's grave, requesting that they never be forgotten.