After the first year. At least that’s what I am discovering while searching for a “I love you” card for my wife.
With the set of cards in front of me, I see birthday cards, boyfriend/girlfriend love cards, engagement card, wedding and first anniversary, then nothing!
Love has to be undusted regularly and the card business indicates that we are not doing it often enough. So go out, buy a card, flowers. Wherever you are just say “I Love You” presenting your gift, and wait for the result, heart drumming.