It all depends what method you use.
In your case you just added the image one after the other, and there area some line returns in there that are causing the drop.
If you switch the content editor to text mode, you can see them as <br/> tags usually.
But the method you used is non responsive, which means it does not adapt / scale when the browser gets smaller.
You need to decide what needs to happen on mobile devices (small screen like a phone), should the image stay in two columns and scale down, or should they switch to a single column and scale down.
The easiest thing you should try first, is add your image using a WordPress gallery. You click add Media, select create gallery, select your 4 images, ad the gallery and select 2 columns. That should do what you want automatically.
Or else to have more control, you can put your images in two columns, created with divs using the weaver column classes as explained here