Hi Bernadette, the genetic vs upbringing debate has been around for years. If some substance like tobacco is inherently physically addictive then IMO genetics has less of a part to play. I think that might apply to some drugs as well. But inherited mental illness or instability might lead to using as a way of self medicating.
Alcohol is a slightly different as it's been integrated into society, and the majority never get addicted. So my guess is that alcoholics do have a strong genetic underpinning. But it doesn't have to be one or the other. Like many things, it's probably a lot more subtle.
I've always thought that no matter what your genetic make-up a strong loving upbringing can help you make the right decisions.
Sorry to get all theoretical on you, when you probably wanted to process your latest thoughts about your XBF. Congratulations realising all your wishing couldn't change him moving on with your own life.