The constant of life is change.
Your wife and you see life very different. Her body has aged and her sex drive also goes down with age. Then how do you cope with these changes?
If you make her wrong and you right, it will cause more drift. Take her out on a date, go dancing, or some activity that you both did together. Leave her love poems on her pillow/car/fridge. If you do the same over and over then you will get the same results. In long terms it is very easy for the union to become nasty and distant.
Know that the only one that you can work on is you. Your self-love and self-worth are of your own doing, how you see you in life will determine your happy state, not her.
She can’t have you be happy, that is your job for you.