The flames of your love can only take so much dousing with water before the fire goes out. Stir up the embers, take the action God requires. Therefore, it should not be a mystery as to why love dies within a marriage. When these problems go unresolved in your relationship, you slowly drift apart. The love slowly dies.
Some couples do both.
They do nothing to stoke the fire of their love, and they are dumping water regularly on what's left. They wonder if they could ever rekindle the matrimonial fire. Yet, when you start asking these questions, you are on the right path. Return to your first love with Christ. I have never seen a marriage that was in trouble where the two individuals involved weren't in need of spiritual renewal.