Whatever you do, don't imagine your OTP old and greying.
Don't imagine them going out to dinner for their Fiftieth Anniversary.
Don't imagine them going to a small family restaurant that's special to them.
Don't imagine a Barbershop Quartet coming in and serenading person A as person B sits back and watches their reaction with a smile.
Don't imagine person B holding out their hand.
Don't imagine person A taking it.
Don't imagine your OTP dancing around a small restaurant to a serenade of Let Me Call You Sweetheart in their old age.
Don't imagine other couples joining them until they've got the waiters, waitresses, and cooks dancing too.
Don't imagine person B singing the words in person A's ear.
Don't imagine them beaming at each other happily.
And, if you want to keep your sanity, don't imagine person A sitting in a chair at a table all by them self, smiling at their waiter, and saying, "Today would be our Fifty-first."