Wow, 51 years, congratulations! We are only at just short of 36, but plan to give you a run for your money! :)
My wife would say that three things help:
1) I still always open the door (especially the car door) for her.
2) We follow my granddad's advice (given on our honeymoon trip): "Never forget to kiss the cook!"
3) We found we were comfortable praying together -- even before we realized we were in love -- and we have never stopped...
~~~~~~~~
May you reach that "Golden 50" -- it's a very good start!! '-)