Actually, you know what? I've was subject to years of physical and emotional abuse by all of my parents (including stepmother and stepfather, I rarely had food growing up, I lived in squalor, and my mother even lost my house when I graduated high school. I may not have been molested, but my older sister certainly was. We were terrorized on a daily basis by one of my mother's long term live-in boyfriends. My mother even married a man she met in a mental institution. My father (who is the relation to my half sisters) is and was physically abusive my entire life.
To say that I haven't an idea of what you went through is way off the mark. I actually have a really good idea of the troubles people can go through. So you're using that excuse toward the wrong person.
If anything, I was being supportive of you and trying to give you encouragement so that you try harder. I had issues with trauma myself that in the past few years have made great strides in overcoming and I'm a much better person for it. My own confidence and self esteem was so low that I was on the verge of suicide, real suicide, not threats, for most of my life.
Stop eating and stop using food as a coping mechanism. One of the most important things that has helped me move on has been working toward the things that I want in life. The more that I've achieved the happier I've become and the more accomplished I feel.
As for you nutritionist, he gave you that target because he knows fat people have very little willpower and judging from your post I can wager he picked that up in you. Obese people can live on a diet of 500 calories. It's actually a suggestion that doctors try before people op into gastric bypass surgery. I honestly felt that you couldn't adhere to such a strict regimen and wants you to ease into a more strenuous one as time passes, but in my experience, that never works for other people.
As for the antidepressants. I think they're poison. I've struggled and continue to struggle with severe depression myself, but again, the more I do for myself, the quicker the periods of depression are in my life. I find myself only getting depressed at this stage in my life if I find myself procrastinating on something that I must do for myself. Antidepressants can be very damaging to your body and brain chemistry over time and I suggest you go to therapy and learn to deal with your trauma so you can eventually go off of them.
Stop playing the damned victim in all of this. I've been through similar situations just as you have and I know that there is a brighter side to things. You just have to stop making excuses and living in the past, it's the only way to move forward in life. Literally think about just what you want and have to do for that day and do it without procrastination. Set goals and execute them. Keep lists if you must, but just execute those goals.
As for my younger half sister, she is pretty lazy. She's 22 and has only ever worked two jobs where she only ever worked 1-2 days a week. She came over to my house somewhat recently and ate all of my cookies and party mix when my girlfriend and I had to run errands. So yeah, it is her fault for not being able to control herself. Frankly, between how my half sisters and I were raised, my older (full-blooded) sister and I had it much, much worse on a day to day basis. I am in a position to judge.