❗ UPDATE: The Sims team released an emergency patch to correct this issue. Please be sure to backup your save and update the game via Origin.
If you’ve updated to the November 7th Game Patch, be warned that there is a serious bug that currently breaks the relationship system. According to SimGuruNick, entering “free build mode” first will completely wipe out existing relationships for Sims.
— SimGuruNick (@SimGuruNick) November 8, 2017
To prevent this from happening, be sure to load your active household FIRST by pressing play on the save. Once you have done this, then continue your game as usual.
If for some reason you have already noticed your relationships have been wiped out, exit the game without saving. If you already saved the game, revert to an older save or use the “Recover Save” feature from the Main Menu. If all else fails, cheat relationships back.