i caught out my JW parents about this 40 years ago. I was living with my lady and invited my parents to dinner--and to meet her.
They said--"you know we cant--because you are not married."
Now--i had already thought up my rebuttal to this...because they socialised openly with my mums sister--and male partner--who had never married and had 4 grown up kids.
i was surprised how quickly they backed down--met my lady--and got on like a house on fire.
We married a few months later--and were together for the next 23 years.