So are the sims naturally monogamous and faithful then?  I remember sims from earlier game versions basically being attracted to anything that moved, no matter what state their relationships were in. So far in The Sims 3 it looks like any sims already in a relationship are categorically uninterested in anything beyond the mildest flirting. Seems sort of limiting (and jarringly unrealistic, even for little cartoon people who get stumped by complex behaviors like walking around an obstacle.)  I saw this thread and thought I'd found an explanation more plausible than that the game was actually intended to work that way.