tl;dr - I've known her for ~7 years or so. Dated for three. She was NEVER this way.

She was actually my younger sister's friend for years. So she was over nearly every weekend (I was at mother's during US economy bottoming out around 2008). I was working two jobs and in college at the time, so I saw her but seldom had enjoy to do much more than sleep or shower before next class/shift.

When she was maybe 14 or so, her father was killed by a hit and run driver. She was over at my mother's when she got the call about it. My mother may be a drunk, but she can open up immensely. My mother, stepfather, lil sister, and I offered any support we could (so far as buying them some christmas gifts because they couldn't afford it without her father). Her mother took up drinking and she bounced around in foster care. She kept texting my lil sister, mother, and I as we were basically her surrogate family and "constant" in her turbulent teenage years. During the time, we texted nearly daily or phone call if she needed homework help or was having a severe bout with depression/anxiety and needed some one just to listen. She started developing feelings for me, but I was disinterested (she was too young and I was having a bit more fun with single/married women in their 40s at that time). Right after she was 18, I realized she was more than just my "non-blood sister". Things evolved from there to friends testing the waters, to full on dating just before her 19th. During this time, I can count on one hand then number of times that she drank or smoked. She was HUGELY against drinking as the pain that foster care caused her because her mother took up hardcore drinking. With smoking pot, both her brothers and sister smoke multiple times per day. She tried maybe three times when she had her "it's cool to smoke" friend, before that friend was arrested for shoplifting (LoL), which scared her away from that friend.