I see, but if you get the chance to fuck someone, can you like do it again anytime?
No.
You repeat each loop a few times with the members of the household, leading to repeating scenes and unlocking more for some scenes as well.
or do you have to wait until the story progresses with that person until you can fuck again?
This does happen, as part of the timeloop mechanic and plot, where you unlock progressively more with some scenes and some variations of others.
There's a lot of repeating things, but that's by design, and Llamaman has done it in such a way that there's no real grinding to it, just what's necessary to advance the plot and progression of the characters.