Board Thread:Speculation House/@comment-24.247.91.107-20140511154823/@comment-32856285-20150222063740

My theory:

(deep breath) Qrow and Summer use to be a couple. With the disappearance of Yang's mom, plot twist: Yang's mom turns out to be Qrow's sister Raven Branwen, Summer decides to leave Qrow for Taiyang in act of sympathy. Because of this dark event; Qrow and Taiyang have a dark tension between themselves, and when Qrow soon hears that Summer had died he blames Taiyang for it and decided to distance away from him.

Cut to lil' Yang and Ruby being attacked by Grimm, Qrow saves the both of them. The reason why he did this? It's mainly because he loved Summer so much that he could not bare the thought of losing her only kid.

Having chastised Yang for reckless thinking, he took Ruby away for awhile until she could defend herself as he couldn't trust Taiyang anymore. Jump to almost nearly the beginning of RWBY, Ruby has learned all she could from Qrow and is able to see Yang/Taiyang again.

The rest: you know.