LiteraryLark-I am so glad that you've expressed some of your fantasies here!
It is scary when we can't control what is going on in our mind.
I think it's good you want to tell your new T but don't be to hard on yourself if you are unable to tell them about it during your first session. I had to build trust with my T before I could start sharing things with them.
Talking with others IRL (including your T) and posting might help set you free. I want to hug you right now. Surely these fantasies are an outlet for some very intense pain you are feeling. Maybe things would be worse for you if you didn't have this outlet. I don't know.
Just wondering, do you read a lot? Your username LiteraryLark makes me think that you do. When I was a teenager, my imagination was not as vivid as yours. I would tend to occupy my overactive mind but reading novels.
I am not an expert, but I think our addictions are symptoms of our illnesses. For instance, when I am depressed, I binge eat. The only way for me to stop binge eating is to recover from depression. If I try to stop binge eating but I am still depressed, I just get more depressed about not having any control over what I am doing to myself. I plan to follow your future posts. I hope things get better for you!