Siblings fall out ALL the time, especially when there is a large difference in success or just in the way they live their lives, plus siblings know so much about you, that when y'all fight, they can say or do the things that hurt you the most.
. My brothers lived together back in 03/04 and some serious shyt went down, they fell out with one another and didn't speak for close to three years, they weren't at holidays together, the only time in that period they spoke was at my college graduation. It took a lot of work from me and letting time pass before they started speaking, they still don't kick it with each other like they used to, but they're cool now.