I've had this occur with sims I make and with sims I download. It's very rare but unfortuanly it does happen. Some sims you can set them to the wife of another sim and it will jump back up to roomate. This has been happening since the base game but I don't think anyone else has reported it so I am. It's very aggrevating. Their both young adults I make sure of that.
This issue might happen with male sims as well but so far I've only seen it happen with females. Please fix this with a patch. It's beyond irriatitng.
Have you been using edit in cas cheat ?
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