My (now-ex) girlfriend recently took up heroin use, which led to the end of the relationship, mainly because of the deception she practised about it and the emotionally manipulative/aggressive reactions when it turns out she was actually lying, but also because I just don't find it intelligible as a life decision to make and lost all respect for her. However, when she asks a me to justify WHY I think it's dumb, why it bothers me, why it hurts me to see her do this, and why I'm against it, I find it hard to come up with a logical reason. She can just say that 'well, there's nothing else to do, so why shouldn't I, and why should you care?', and all I can come up with 'Look, it's just how I feel, it's what I believe and if it's not obvious to you then I can't explain it.' This feels less than satisfactory. She has said, and there is some evidence for this, that alcohol is worse than heroin. However I think the studies that show this are more related to frequency and wide-spread abuse of alcohol, compared to the relatively low usage of heroin in society. And heroin is surely FAR more physically addictive in a much shorter time than alcohol is, and has a large impact on behaviour that impacts those close to the user - the trust and security of the social relationship is immediately no longer assured, so there ARE ethical implications aren't there? Can my objections and negative feelings associated with her new addiction be stated in terms of moral logic? Is demanding 'proof' and the reasons for my feelings, which are totally subjective, void in the first place? Is heroin use logical justifiable because of boredom and as an enjoyable pastime unrelated to serious illness? The fact that I have subjective feelings COULD be the result of unexamined assumptions about heroin use and the stigma associated with it, OR it could be that there are very good reasons to feel this, even though I haven't quite researched the way to present the reasoning in a logically consistent way. I am also aware that she is just probably going to use any way to justify her choice and make me seem like a jerk for not supporting her or having respect or compassion for her decision, but it is more for my own peace of mind than to score points against her that I want to resolve this. My other question is, given that we have to live together until we can organise other places to live, do I have a right to protect myself from the imagined and possible consequences of her behaviour (possible unreliability in paying the rent or other bills, possible betrayal through theft) by reading her private messages? I think she has the right to privacy, but I also have the right to protect myself from being lied to. What's the line?