So you really need to take this to a relationships board because between this:

this is the reason I'm seriously considering not having kids despite the fact that my fiancé loves kids which is nice but I'm seriously hating it.

and this:

He called saying that he had a terrible night having to watch the kids alone

It's clear that your fiance and you are not anywhere near on the same page regarding things from "should we have children?" to "whose job is it to watch the children that I did not consent to watching?"

You have ample evidence that your fiance is not putting you first. And he is, in fact, throwing tantrums when your time and attention are not available for him to deploy as he sees fit.

You're NTA in this instance but sort of T A if you stay in this situation because the man you're marrying doesn't really give a shit what you want.