When does a boyfriend become a partner

Yes partners 😊

My DGD and the man who is now her husband lived together for four years. If people asked me if she had a boyfriend, I just said yes.
She referred to him as her ‘boyfriend’ until they got engaged, then she said ‘fiancé’, so we did too.

Allira

There are no rules.

I would refer to them as partners as they seem settled and are buying a home together, but whatever they prefer.

I agree

There are no rules.

I would refer to them as partners as they seem settled and are buying a home together, but whatever they prefer.

Ask them how they want you to refer to them.

Rules not quite the word but I see the OP’s point, esp if the other way round. It wouldn’t seem appropriate to call a boy friend of 6 months a partner.
But no business of anyone else’s. The OP could just shrug off people rude enough to ask

What rules ?
If people ask how your granddaughter is you tell them she’s fine or just broke a finger or been on holiday
If in doubt ask her how she d like you to refer to the man in her life I don’t see how we can help we ll all have different ideas
I always called the man/ men in my life, my partner but it’s what they want

Whatever they want them to be. If they refer to one another as girlfriend and boy friend then that's what they are. If they refer to one another as 'my partner' then that's what they are.