Everyone likes to be acknowledged for the things they do. In established relationships, sometimes people take things for granted. No matter how much someone loves you, everyone has a point where they get tired of waiting to feel appreciated.
What to do: As simples as it sounds, please and thank you does a long way to showing someone that you value what they do. On a deeper level, tell them regularly that you are grateful for their efforts and actions. Support their efforts, and look for ways and opportunities to show them that you are appreciative of not only what they do, but also for who they are.