Honestly, I’m not sure how close they were as friends to begin with. I’m sure they liked each other well enough, and I don’t think it was a chore for them, but I think the public friendship was really just to introduce 5SOS to the 1D fandom. Because whether you like it or not, the vast vast majority of 5SOS fans came from 1D and 5SOS wouldn’t be where they are right now without 1D and the way they interacted last tour.
So last year there wasn’t a lot of 5SOS promo, so 1D did that for them, through tweets, through instagram and vines, 1D fans learned about 5SOS. Now that “friendship” is gone and is replaced with 5SOS doing all of 1D’s regular appearances.
I think there is a lot more to the 5SOS discovery story than “Louis randomly found them”.