What is the term for someone who has always exercised restraint in behaving a certain way but a change in lifestyle allowed the behavior to surface?

Question

Here is my sentence that I need help completing:

He was always emotionally and verbally abusive towards my mom but it never got physical until June of 2014 (that I’m aware of). The alarming increase in not just the quantity of booze he consumed but the amount of time he spent consuming it is _________________.

I am trying to say that he probably always wanted to hit her but never did because he could restrain himself, however, the increase in alcohol is what lowered his inhibitions thereby allowing his emotional abuse to graduate to physical violence.

Is the best way to say it the way that it's written above? I feel like the term is RIGHT THERE but I can't seem to grab it!

Thanks for any insight. I just found this site and am officially OBSESSED.

Answer 1

I guess it can be said in several different ways. Couple of ways I can think of are as in:

The alarming increase in not just the quantity of booze he consumed but the amount of time he spent consuming it is what made him [cross the line]/[show his true colors].

TFD(idioms):

cross the line

if someone crosses the line they start behaving in a way that is not socially acceptable. 
Players had crossed the line by attacking fans on the pitch.

Cambridge Idioms Dictionary, 2nd ed. Copyright © Cambridge University Press 2006. Reproduced with permission.

show one's true colors

Reveal oneself as one really is, as in:  We always thought he was completely honest, but he showed his true colors when he tried to use a stolen credit card .

The American Heritage® Dictionary of Idioms by Christine Ammer. Copyright © 2003, 1997 by The Christine Ammer 1992 Trust. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

Answer 2

An answer reflecting @Gary's analysis:

The alarming increase in not just the quantity of booze he consumed but the amount of time he spent consuming it is stripping away the judgment and restraint he has shown in the past and led to uncontrolled behavior unmediated by his own values.