Then you’re out of luck.
Obsidian relies on this tech for skinning your text. You have to be willing to at least copy and paste some pre-established snippets to achieve the effects you want, even if you don’t understand how they do what they do. It’s not hard, there’s a dozen tutorials for this on these forums. If you don’t want to do this at least, then there’s nothing you can do.
Now, on to the solution. As a fellow fiction writer, I absolutely feel your pain, and the devs were kind enough to provide with the solution. The CSS snippets you’re looking for, ready to use, are here:
They add spacing to paragraphs (not first line indents) both in edit and preview, which provide the visual cue you’re looking for (alter the numerical values to your liking). It has absolutely changed my use of Obsidian and makes writing so much better. I agree 100% that this is mandatory for writing long form if one is to keep his or her sanity 
Just as a side note:
Obsidian is not open source, it uses open standards (which are CSS and HTML), which is why we can reach into many hooks and skin it, and write plugins for it. 