The part broken looks to me on the outside of your fenders, Am I right (I honestly can't tell from your picture)? If so its possible that you've stuffed your tires into your wheel wells while turning and at speed, if so the problem could've been caused by your bump stops! (Are you running extended ones or stock?)
My friend was running -2 offset on the rears with 35s + 1" body lift and he got the tires to touch the fenders while wheeling, turned out his bump stops were shot! Replaced them and never had to worry about it anymore!