I think everybody has, at least once, gotten themselves in a similar situation, where they think they deserve more, because they have given more.
Today I want to discuss this system we have "developed", but to be totally honest this isn't something we have achieved, it's something that dates back to the ice age.
In the religious sector there were-and technically still are in some places of the world- some rituals that are based on this concept. Animal offerings and offerings in general are such examples. If you give the Gods something they appreciate than you will be fine, because you will be on their white list.
In the financial sector there is something we call money. Which we trade, in order to take something else in return. In other words, we give something that we think has great value, so we can have something of equal value. Does that ring a bell? Maybe the "why doesn't he/she love me back, when I've done so much to show him/her how much I want him/her" ? We give something to somebody and we expect another form of this something to come to us, without actually giving this a second thought.
In the social sector- taking the family as an example- this example, at least in some cases, doesn't exist. But in the "fair" society we live in, based on the notion that everybody is responsible for their own mess, it goes something like this. Mum is in charge of the cooking, in return Dad is responsible of bringing money to the house and in return the children should tidy their rooms/throw out the trash and do their homework. If seen less stereotypically, Mum should cook some times and work to bring home the bacon and Dad should, in return, compensate in the way that he cooks some times, too and works.
With this in mind, I need to point out that this is what we have defined as "fair". This concept isn't something we have created, but this is how people are.