Hello @teutonium :)
I am glad to hear you managed to rationalise your drinking habits and start exercising instead! However, being addicted to exercise is not a healthy thing either. But, I do believe you can find moderation. I say this because you were able to stop with the alcohol intake through a really self-aware manner.
Your friend’s story life is heart breaking! I do find that a great, great number of addictions are a consequence of troubled childhoods. The book I mentioned here, for example, The Secret Life is an account of a sex addict, who was abused when he was a child.
Yes, some people do seem to be more prone to addiction and there is strong suggestion that is due to genetic factor. It is a good thing that you are a smart guy who seem to have great levels of self-awareness. Having the understanding that you are susceptible to addiction definetly puts you in disadvantage. Wll done! :)
All the best to you & Take Care!