I can understand your perspective, but I want to offer an alternative view, maybe less bound to societal preconceptions. I married my partner for many reasons, financial, wanting to raise a child together, wanting to share my life with them… But staying married for the rest of our lives is a crazy concept for us. The marriage has its purposes, but we both know that life can change and that we could decide that we had a good time, and that now the time has come to move on. A marriage is less romanticised for us, it has practical reasons. I guess being polyamorous helps with defining new relationship ideas on many levels ;)
I don’t know if this will keep the labels, but you can try to sync your contacts via DAVx5 to your nextcloud instance. Use https://f-droid.org/packages/at.bitfire.davdroid on both phones, this app syncs calendars, contacts and notes. In the setup it should be enough to login via URL and credentials. If you run into problems with this setup, let me know, I can try to assist you :)
Once you got that set up, it is a neat way to keep your contacts backed up and synced with other devices like a PC. If you want to dive further into the syncing without relying on Nextcloud, I recommend Baikal.
Good luck!
Algovir macht nicht abhängig und soll als Bonus auch noch vorbeugend gegen Covid wirken.