Why does removing 1 line remove an entire surface even if they are straight

titel, the line is on the roof, ive read on another post that it not entierly starght or something
smaskigt hus.skp (697.6 KB)

The edge you are referring to is required for the faces on either side to exist. The gable end edges are not in the same line. You can see that easily if you temporarily extrude the roof faces with Push/Pull. I’ve done that here and you can see there’s a little gap opening up.

Easiest fix would be to erase the existing edges and redraw them as single continuous edges. You only need to erase the ones on the gable ends and then redraw them as single edges.

i used this and it worked good but i also removed some other lines, i removed these same line on the other side.

the drawn lines are where the lines used to be.
smaks.skp (603.7 KB)

You have the same sort of problem on the bottom surface as well and they need to be fixed in the same way.

Instead of taking the time to fix all of the misaligned geometry, it might make more sense to start over and use a different workflow. If you draw the end of the house first, extrude it, and then draw in the lines for the ends of the roof before pulling the thin gable face out, you won’t have any of the misalignment. Just make sure that all of the edges are straight.