Hi Conner. I am an Excel user like you.
It seems that there may be a couple pertinent questions. The first is why is Excel dividing it into separate pages, and the second is how to return it to normal.
On the second question, on the Page Layout ribbon in the Page Setup section select Breaks and then Reset All Page Breaks. Hopefully that will remove the dotted lines/page breaks that you see.
The first question seems the more difficult. I would start by checking the other page layout settings including the paper size and margins. If one of those somehow got changed that might explain why Excel is dividing up the pages the way it is.
I have not experienced this problem or seen where anyone else has. So hopefully it is just a simple setting adjustment.