Spacing on Posts / Line Breaks / Fonts in General

Hey there, hopefully someone can help me out on this. I have a blog here: https://stylusmagazine.com/discovietnam/ that I’m trying to do some simple posts on, but the text keeps messing up. All I want to do is have the five lines on the post, with one that is bolded (the second line). Each time I go into the html of the file, however, things are added that I never put in there (like massive amounts of <div align=center>’s, etc.) and whenever I go back to looking at the post, something is wrong (the new problem seems to be that a line jumps up to join a previous line, deleting the line break that I’ve put in). Why doesn’t wordpress’ visual editor allow me to see exactly how the post will look on the page? Why is it so radically different in between the time I hit save and when I go to look at the post? Is anyone else having these sorts of problems?