Receiving healthcare through partners social security?

I think you mean applying for EU Citizen Registration.  That is different from an NIE which is only a fiscal ID number and carries no Right to residency

A spouse is covered for medical care but I am not sure how that works with a non-married couple. I believe you will be cover though

Thanks so much for your reply, very helpful thanks. We'll go to the office and speak to them next week

And yes you're totally correct, I've been getting muddled with NIE and EU register for residency

I (UK national) have been paying into the Spanish social security system (it costs 300€ a month for self-employed); I get a Spanish health card and an assigned medical centre.
My wife (who is Japanese) applied-for and received her health card  by virtue of my registration, she does not work and she has seen the Doctor several times.
The only possible complication is that you are not married, I imagine that will be OK under European law but you´d best check it out, maybe someone here can help. You may have to register as being in a civil union, a friend of mine did that here in Spain,  it is called "pareja de hecho".

Thanks so much, I'll look into pareja de hecho, I haven't heard of it. So much to learn!

Georgia

If you make an internet search on ‘spain living as a couple rights’ you will find pointers to a lot of info