Relationship

As soon as a character (Sim or pet) meets another they accumulate relationship points. The amount of points two characters have for each other and their life stages determines how they can interact. Interacting with each other builds their relationship score, while neglecting them will result in a decline of the relationship score.

In The Sims 2, each character has a daily relationship score and a lifetime relationship score. Over time, two characters' lifetime relationships will build up as long as they continue to interact. Sim relationships could also go up or down with the use of cheats.

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 in the end is higher.

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 a close friend.

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.