When you pay attention to a relationship, invest time and energy, gratitude in return is a natural reaction. If there is no gratitude, then over time the desire to do something for him disappears.
The most common mistake partners make in long-term relationships is to take caring and affection for granted. For example, a man brings money to the house, and instead of caring he gets reproaches.
Gratitude is the strongest incentive for both to keep trying. It works as a positive reinforcement. The simplest example: a man has not given flowers for a long time, and suddenly he brought a bouquet to the lady of the heart. Offended by the long lack of attention, the woman wrinkles her nose: "Ugh, daisies, I love roses!" - and will not get a chamomile or a rose next time. Or she can bloom in a smile and sincerely thank for a beautiful gesture - and after that she will see roses, tulips, and exotic orchids.
Gratitude works in a special way. Hearing it, we perceive it as a compliment to our own personality. Who doesn't want to hear compliments every day?