Re: Sims 3 relationships
@ohsehun_094 From what you describe, it sounds like your sims are corrupted to some extent, and I'm not sure whether it will be possible to recover this save. If you want to try though, the first thing to do is to delete the five cache files in your game folder in Documents. They should be deleted regularly anyway, and while you're troubleshooting, be sure to delete them every time you quit the game. For reference, the files are:
- CASPartCache.package
 - compositorCache.package
 - scriptCache.package
 - simCompositorCache.package
 - socialCache.package
 
Once you've reloaded your save, go to Edit Town, evict your sims, and place them back in their home. This will erase their promised wishes and opportunities, but it will preserve their jobs and relationships. Then use "save as" to rename the save (so you have a backup), quit without saving, delete the cache files, and reload. The family trees may be a lost cause, so check their relationship panels instead. If they're all still dating that one sim, have one of the others break up with her and see whether it affects any of the others' relationships. If not, you can have them all break up except for the one who's supposed to be dating her, save, quit, clear your cache files, and reload.
By the way, if you don't want the negative moodlets, you can remove them manually. Bring up the cheats console (crtl-shift-C) and enter "testingcheatsenabled true" without quotes. Then crtl-click on each moodlet you want gone. (I think it's crtl-click, but try shift-click if it doesn't work.)
If one sim's breakup affects another, then without mods, there probably isn't a whole lot you can do. The only other way to keep playing the family may be to save them to the bin, save the house separately if you want to keep it, and place them in a new save. They'll remember each other, but their outside relationships will be gone. (You could also save the girlfriend and place her in the new save, but your active family wouldn't know her.) Be sure to quit to desktop and clear your caches before starting the new save. If you switch from the Main Menu, data from the old save can transfer to the new one, and that can include corruption.