sexuality

@derplitfrom my understanding of the game, they will flirt more with what ever gender you have them flirt with.  So, for example, if you want Sim A to flirt with males, then the more you have them flirt with males, the better your chances that they will flirt with males autonomously.  It seems to work that way in my game... the longer I play with a Sim the more likely they are to behave in the same way I had previously controlled them  
This is kind of like the more you have your Sim paint, the more likely they will be to paint on their own. 🙂

@derplit, they added the gender preference in a patch a while back, so it works like @PugLove888 said. 🙂

@PugLove888 @SqueamishNerd Even with whatever gender preference system the game is currently using it's still not 100% effective. I've had Sims who are either completely straight or completely gay try to do autonomous romantic interactions with other Sims of their non-preferred gender. For example, Sims with a high level of Charisma will autonomously attempt to do "Enchanting" or "Flirty" introductions with other Sims of their non-preferred gender. It's especially annoying because it instantly creates a "Romantic" relationship (i.e. a relationship with a Romance bar) with a complete stranger and it takes forever for that relationship to naturally fade from the game.

@SqueamishNerd Lol no wonder it seemed like it was taking so long! xD This is why I resorted to using mods to make them go away.

@RandomBuzziness,  @SqueamishNerd , and @derplit  yes, it isn't 100% fool proof, but it does help.  And in this too, it is rather like painting -- your Sims will eventually be more likely to paint on their own if you direct them to paint often, but even Sims you never direct to paint will still sometimes give it a try! 😃😉