Do I ask for it off or call in sick?

My fiancé works a ton of hours and rarely takes time off. I had a co-worker already request the week of Christmas off. Then we had someone go on emergency maternity leave. I kind of assumed that I couldn’t take any time because we have to cover each other’s desks.

I specifically told my fiancé that I had to work(I’m 100% remote) and he said he’d probably work too. Then today he asked if I was off next week because he was.

My question is, I know it’s short notice but do I ask for Thursday and Friday off? I’d like to spend some time together. Or do I just call in sick?

If I ask for time off what do I say?