Has your partner equipped your Promise Wristlets which is needed for your quest? And are you both in a party together? If I remember rightly back to my own wedding quest both you and your partner have to equip the engagement wristlets and then speak to the npc at the same time while in a party. Yeah it's weird like that.

Also reading this page (which includes a transcription of the in-game journal) it mentions in order to proceed you both need to have finished all previous requirements in the quest, so maybe your partner is missing something? (Like, have they gone to the GSM's Guild and showed the ring to the npc there?). If they are missing a step, look back through their journal to find what part they're missing and compare it to that page so you can see what you need to do to proceed.

Anyway, congratulations on your engagement! I hope you and your betrothed can overcome this obstacle quickly.