Not all of them act this way. Some are very good at hiding it but I believe eventually they do make a person act that way. Drugs will always show their true nature to the people who take them. These people who take them (the people we care about!) are not living for the quality of life anymore, they live for their drugs.
I didn't know my ABF was using entire month of August and I just found out 2 days ago. He tried to lie to my face and tell me I'm a horrible person for believing that he was and then he switches it around and complains that I should have known sooner! Oh they can't make up their mind about which bullsh*t story they are going to use next.
My ABF claimed he couldn't be with me because he suspected I was using too (the mentality that if he does it, everyone must be doing it) and cheating. I wasn't do neither and he tries to make me beg for forgiveness and apologize. As if.