Question: [![enter image description here](https://i.stack.imgur.com/asb8h.jpg)](https://i.stack.imgur.com/asb8h.jpg)

When I add edge loop to this, angle is already broken. How do you make 1 and 2 edge loops parallel each other?

Answer: 
Whether or not you have just created it, if you want to make an edge-loop parallel to an adjacent one, slide the loop with `G``G`. Now hitting `E` will make the loop parallel to one side or the other. Hitting `F` will flip which side. Hitting `E` again will revert to the default behaviour: interpolating between its original orientation, and whichever edge you are sliding towards.
Assuming you used `CTRL-R` Loop Cut

In edit mode

After loop cut is finished. Scale along an axis with number `0`. Hopefully X or Y or Z will work.

`sx0`

`sy0`

`sz0`

or use

[Knife Cut] `k`with cut through ON `z` 

the keystrokes are also indicated in the 3D View 

[![enter image description here](https://i.stack.imgur.com/k5hcG.png)](https://i.stack.imgur.com/k5hcG.png)

Knife cut image above. Unfortunately the screen capture did NOT capture the little knife cursor. The lower left shows the Knife Topology tool panel.

youtube has video tutorials on knife cut which will save you time.

BSE can be searched for Knife Cut.