Okay so...

Did it ever occur to anyone in this fandom that what if Qrow had a crush on Summer when they first met? Like, what if Qrow's first relationship was with Summer while Tai-Yang and Raven were together? But then when Raven left Tai-Yang and baby Yang, Summer felt sorry for Tai, and started to help him out in raising Yang and such. But the more they spent time together, the further apart Summer and Qrow got until Summer fell in love with Tai and vise-versa.

Qrow and Tai may have had a bit of a quarrel over it, but wanting to make Summer happy, Qrow realized it was best Summer be with Tai. This is where his drinking begins, but not to where he's constantly chugging down alcohol every second.

No, Qrow's actual drinking problem starts when Summer died. Imagine, if you will, the woman Qrow's been in love with, and allowed to get away with his best friend, has died. He probably wasn't even there when it happened and he regrets every single second of it. 

But to keep the image of a good Huntsman and a good uncle, Qrow keeps doing his missions, as well as deciding to teach at Signal Academy with Tai-Yang.

If y'all are still skeptical, let's take a look at how close both Summer and Ruby look! Ruby is basically the spitting image of her mother and Qrow clearly sees this! What if that's one of the main reasons why he took her as his student and taught her how to use a scythe? What if Qrow felt that he would find some form of happiness by teaching the daughter of the woman he once loved in an effort to make up for lost times?