If you feel like partner is the right word, then I'd back you up on that.

Partner is great and is non-gendered (in English). You could also go for the classic or boyfriend / girlfriend or "I'm in a relationship" or significant other. They all work but you do you. If you feel like partner is best and you're romantic interest is cool with that title - go for it.

I once panicked introducing a friend and said "lover". Don't think I could have made everyone involved more awkward if I had tried.

I like primary. Secondary sounds like you're ranking people however.

Let me know if you figure it out. Not that I'm participating any longer, but I am curious.

Consorts?

Partner is the word.

If your friend thinks there's a better word, ask them what it is.

Call them whatever you want. Your relationships your choice. There's no need to gatekeep every little detail ffs.