I don't think it's unreasonable - from a professional perspective - to link someone's career advancement/prospects to the behavior of a SO (or even a Plus-One) at work events.
If your SO is such a hot mess that they can't keep it together and behave appropriately at a work event (whether through ignorance, illness, addiction or just being flaky), then sooner or later that is going to create chaos in your working life. And if you were bringing people who behave inappropriately who are not even your SO, just a date or a family member, that would show a profound lack of judgement, or boundaries.
Leadership/high-responsibility positions + personal chaos/distraction = bad for the bottom line.
So, good for OP for saying "no" and hopefully this will pay off in improved family boundaries - and work prospects - in the future.