Relationships are built from a market. each one is looking for the other partner by their specifications or things they wish to find in the other. the same consumers theory in economics. you like Pepsi when you don't find it you can replace it by Coke or another. you also can stop taking the alternative. this is the market works. and this is how the market of relationships works also. you love someone and things work good you will be happy, if not you will look for a new alternative or stop searching until another time.. Market.. demand and supply.. so choose carefully!