BYRNE AND CLORE 1970
We enter into a relationship because the individual concerned creates positive feelings in us, which makes them more attractive to us in the following ways:
We like some individuals because they provide us with direct reinforcement (they make us feel good)
We like some people because they are associated with pleasant events. These feelings lead to a positive (if they make us feel happy) or a negative (if they make us feel unhappy) evaluation of the individual concerned.