Going steady
In The Sims 2, Going Steady is an interaction only used by teenaged Sim lovers. This means that they will pay attention to their only love. Usually, this means a Sim will have a girlfriend or boyfriend, though the game does not use those terms. If a teen is caught cheating by his/her Steady, they will have the option to "Break Up" with them. However, the player must work very hard to bring the relationship up again. Since this relationship is limited to teens, it will be broken when one of the Sims involved grows up.
In The Sims 3, the interaction is available to Sims from teen to elder. A successful proposition to go steady sets the boyfriend/girlfriend relationship between two Sims. To propose going steady, the Sim has to be a romantic interest first. A certain amount of successful romantic interactions will give the players the option to propose going steady.