When you are spending level up points, there is a button that lets you reset. Does that mean all the points you've already spent will be gone then?

I know this seems silly to ask now but I don't want to risk doing something stupid.

I acquired a pet that had a sizeable amount of unspent level up points, I have not used it in battle yet ('cause I am not high enough level) so it has not earned more points henceforth so will I lose all the points that I already used?

They never get lost, don't worry! It just means they get changed from Spent to Available, you can then use all the points your pet has earned up to that point in any new way you want.

So even if I have leveled up a pet, battle after battle, I can still regain the points back so I can reallocate them? Interesting..thanks.

Yeah, or if you get a pet from someone else, you can reset the points from what they had, and choose your own point spread! Same with Proficiencies, they just get more expensive to reset if you have a high level pet.