Relationship

As soon as a character (Sim or pet) meets another they accumulate relationship points. The number of points two characters have for each other and their life stages determines how they can interact. The score will go up or down depending on whether interactions between the two are positive or negative, but neglecting a positive relationship will result in a gradual decline of the relationship score. However, a negative relationship score will gradually improve until it reaches zero.

The Sims
In the initial release of The Sims, there was a single relationship bar which ran from -100 to 100. The Sims: Hot Date turned this into the daily relationship bar, and added a lifetime relationship bar. While this arrangement was not put into The Sims Deluxe Edition, it was carried forward into subsequent expansion packs, and into The Sims 2.

Two Sims would become friends if each one had a daily relationship of at least 50 toward the other. If they also had lifetime relationships of at least 50 toward one another, they would become best friends, though this would not be indicated in the relationship panel. Once an adult Sim's daily relationship with another hit 70, a successful romantic interaction between the two would result in a crush. If the lifetime relationship was at least 70, it would result in love. This was carried forward into The Sims 2.

Once two Sims had any kind of relationship, the lifetime relationship between them would build as they spent time together on the same lot, even if they didn't interact. However, this increase in lifetime relationship would come at the expense of their daily relationship. Every so often, the daily relationship would drop by two points, and the lifetime relationship would increase by one point. In addition, some interactions between Sims, such as giving gifts, would affect the lifetime relationship. Lifetime relationships tended to be highly stable over time; even if two Sims went a long time without interacting with one another, the lifetime relationship would barely be affected.

The Sims 2
The Sims 2 retains the daily relationship score and lifetime relationship score that were introduced in The Sims: Hot Date. However, characters' relationships with one another no longer change simply because they spend time with, or around, one another. In The Sims 2, the lifetime relationship score gradually approaches the daily relationship score, so over time, two characters' lifetime relationships will build up as long as they continue to interact enough to keep their daily relationships high. Sim relationships could also be raised or lowered with the use of cheats.

In The Sims 2: Pets, pets develop relationships with Sims and other pets. Sims gain relationships with pets by doing positive interactions, such as praising, playing, or giving love. Negative relationship points are given when a Sim scolds or yells at a pet. When teaching a pet tricks, the relationship goes up and down, depending on how fast the pet learns, but will be higher in the end.

Casual

 * Just Met: The two characters have met, but have not interacted enough to have a definite relationship. Daily relationship will be close to zero, though it may be positive or negative.


 * Acquaintance: The two characters are not friends, and the one whose relationships are being looked at does not consider the other an enemy. The relationship scores may be positive or negative. This is independent of family relationships; parents and children can be acquaintances if their relationship is neither strongly positive or strongly negative.

Inimical

 * Enemy: For the PC version, the Enemy relationship is set if each of the two characters has a daily relationship of -50 or less toward the other. Breaking it requires a positive interaction between the two once one character's relationship score has risen above that level.


 * Console versions of The Sims 2 also have Arch Enemy. For these versions, the Enemy relationship requires a daily relationship of -15 or less.

Amicable

 * Friend: Each of the two characters has a daily relationship of at least 50 toward the other.


 * Best Friend: If each of the two characters has a lifetime relationship of at least 50 toward the other, this relationship will be set when they have a positive interaction.


 * Best Friend Forever: "Best Friend Forever" was introduced in The Sims 2 FreeTime, and reportedly happens when two characters have been best friends for a certain amount of time.

Romantic

 * Crush: Daily relationship of 70 or higher.


 * Love: Lifetime relationship of 70 or higher.


 * Going Steady: only used by teenaged Sim lovers, and must be proposed by one of them.


 * These relationships will not automatically be lost when the relationship falls below the required level.

Contacts and Fury
Contacts and Fury were introduced in Nightlife. Contacts are Sims who have heard of a Sim from a mutual friend (They can be playable or Downtownies). They will phone that Sim asking to go downtown on an outing or date. The relationship between your Sim and the Contact is given a boost for a short period of time. Their picture will be blue.

Sims can feel fury at Sims that had a hostile interactions with them. It also occurs when Sims are caught cheating. It decreases the relationship drastically while it's in effect, putting both Daily and Lifetime scores below -50, depending on the "offense" committed. The target of a Sim's fury will have a red overlay on his or her picture. The amount of red roughly indicates how much longer the Sim will remain furious.

Pets' Levels
Cats Dogs
 * Mine: The cat claims ownership of the Sim or pet; similar to Best Friends
 * Master: The dog is loyal to the Sim or pet
 * Pack: The dog recognizes the Sim or pet as a member of his pack; similar to Friends.
 * Best Friend: The dog treats the Sim or another pet as a close friend.

The Sims 3
when you become friends, you can ask to go out to dinner. At the dinner, you can eat the other sim. If you choose not to, if you propose to engage, then at the wedding, you can eat the other sim.

Marriage
Sims require a high relationship to become married or joined, but the state of being married or joined is not lost autonomously if the relationship score declines.