In Sims 3, if you ma gay Sims, they pretty much always stayed gay - even if you stopped playg them for a while.
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SIMS 4 MA MY GAY SIMS STRAIGHT
I do not have the full story mted to memory, but some batn of nfn (sign document nsistenci, or g an old sign document) and the sexualy of the guy charge of the thgs (he was gay) is the only reason this happened the first place. Inially the game was not gog to have gay upl or gay romantic teractns whatsoever! By sheer cince, the game lnched wh gay teractns as a possibily.
Thanks to u/atedwater for this, the actual story is pretty much what I said above, but wh the add twist of an earlier versn of the game at E3 beg ma wh the outdated sign document, accintally showg off a gay kiss, and changg thgs forever! Though homosexualy was an accint, there was a mercial for the game featurg a man a club flirtg wh a woman, before sudnly beg drawn to a man!
Gay Sims were fally allowed to get married! Their preference is termed by teractns (so if the player teracts as a male wh a male NPC, that male NPC gradually "be gay" and will not outright reject the sim unls they have prevly "bee straight") and n change over time, based entirely on player directn. Sims are not tonomoly gay or straight wh other sims until the player tablish their sexualy by hand.