Some simmers are reporting that ever since the latest Sims 4 Update their relationships in the game are being wiped out for no apparent reason.
SimGuruNick has confirmed that this is in fact an issue that’s currently being fixed by The Sims Team. Until then, here’s a workaround that he provided which helps you prevent relationships from being wiped out:
If you are loading into an older save on the new patch, please ensure that you press Play on your active household first, do not start by entering free-build mode on a lot. If you load into free-build mode first, you could potentially wipe all relationships in your game. If you encounter this issue make sure to exit without saving. If you accidentally save, you can use Recover Save (from the Load Game menu). Our engineers are actively investigating this issue, thank you for your patience.