Romantic interest in TS4

There seem to be certain thresholds in the way sims express romantic interactions. Casual romantic options are available to sims that don't have a romance bar yet or that just started out romancing a particular sim. As that romance bar fills up more options will become available. However, while 'romantic interest' is a casual level where sims won't react (too) negatively when their interest is using the more casual romance interactions on other sims, once you have used romance options like 'going steady', 'Ask to be boyfriend/girlfriend', 'Propose', and 'Marriage' those sims will react very strongly when their significant other romances another sim. So part of the way TS4 handles romantic interest depends on how far along and which choices have been made. The flirty mood does complicate things just as the romantic trait, the free love NAP, Vampiric Charm/Allure/Fascination, the Infatuate spell, and setting romantic interactions as encouraged club activities. There's also a hidden value that determines which way your sim swings depending on the frequency you use romantic interactions on a specific gender. And the Serial Romantic Aspiration, when completed, will grant your sim the Player Trait, allowing them to romance anyone with impunity.