We are brought up to thank people when they do something for us or give us a present. It makes them know you appreciate them and is good manners. Likewise it makes someone feel good when another person says they value their company or compliments them. Sometimes people in an established relationship can forget to regularly show their appreciation. This leads to feeling taken for granted and is not good for a relationship.
It may be that one or both parties no longer notice all the other party does around the house or in terms of providing financially. Sometimes a person assumes their partner just knows they are appreciated so they don't take time to express the sentiment. At other times one partner feels the other is only doing what society expects of them and so they see no need to show appreciation.
Keeping a house clean takes a lot of work. Providing meals, looking after children, keeping on top of all the bills and maintenance of a house and garden all involve lots of planning and effort. Employment can involve long hours and be stressful. One or both partners may also care for their parents or another family member. The list of responsibilities goes on.
When partners thank each other and make favourable comments about tasks done it shows they have noticed the efforts of the other party. When they work on things together it makes tasks easier and perhaps even fun. Paying the other person a compliments shows you notice them and will boost self esteem.
As well as verbally saying thank you or paying a compliment, appreciation can be shown in other ways. Sometimes a little note or card shows how much you appreciate your partner. Perhaps you could give your partner a few flowers or small gift such as a candle, bar of chocolate or other treat. It is becoming more common for men to receive flowers these days so this is no longer a gift suitable only for a woman.
A treat you will both enjoy could be arranged as a way of showing appreciation. Going out for a meal if you don't do this often would be nice and gives you time to focus on each other as you talk. Suggesting a trip to the cinema or a walk along the beach as you eat an ice cream shows you want to spend time in your partner's company.
When a couple are busy and have been together for years it is easy to forget to express gratitude and pay a compliment. However, making the effort to let your partner know you do appreciate what they do and who they are helps to keep the love alive.