I think that one thing that needs to be added to TS4 is open relationships. "Ask to be in Open Relationship" should be a Romantic interaction once you have some amount of pink in the relationship bar (maybe 20? 25? 30?) that adds a new relationship-thingy (ex. Boyfriend/Girlfriend, Married, etc.) called "Open Relationship" (and of course in Mean there would be something turning it back to a normal relationship). The effects would be as follows, using Sim A and Sim B as our examples in an open relationship, Sim C as Sim A's romantic interest, and Sim D as Sim C's other romantic interest: If Sim A flirts with/woohoos with/etc. Sim C, Sim B won't be jealous/sad/whatever; if Sim A and Sim B are romantic in front of Sim C, Sim C will not be jealous/sad; if Sim C and Sim D are romantic, Sim A will not be jealous/sad; and if Sim A is noncommitical, while they have a boyfriend/girlfriend/spouse that they are in an Open Relationship with, they will NOT have the Tense moodlet (I forget what it's called) coming from being in a relationship - maybe they even have a Happy moodlet for a bit after getting married/getting a boyfriend/girlfriend, "In Love, But Not Tied Down"! This would be a great addition to the game.