It was about his addiction issues in the past nothing to do with his old girlfriends
Even then, he probably went through some tough times with the addiction and might not want you have to explain them since it will probably bring up some feelings he wishes not to feel again.
Thanks for the MHO :)
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A brag about what?
He's painting the picture that he might be a little "dangerous". Girls like dangerous dudes. You know, guys that live on the edge and can handle themselves.