Hello Anon,
Thank you so much for finding the courage to seek help, and finally treat the problem from the roots!
I would love to help you.
Hmmm.
Ok, so. You need to feel extremely comfortable with your psychotherapist (if you are seeing a psychiatrist, same rule applies [aside from your psychologist]). Communication between you and them will become vital to your recovery. You need to build a solid foundation based on trust.
Accept the fact that relapse happens. When you have been living —- or are accustomed to —- to such a “normal”routine, when you start to do things differently, and find different coping mechanisms, your mind and body are in a complete state of shock. When, and if you do relapse, do not be afraid to talk about it. Both your family and psychologist will help you.
Identify your triggers. Once you start therapy (not sure if you already started), your therapist should talk to you or guide you into realizing and identifying what your triggers are. Be comfortable, and accept them as they are. The more you resist to those changes and reality - the harder recovery gets.
Don’t take anything personally. Whatever your psychologist wants to talk to you about, perhaps childhood, or teen years —- perhaps he is finding stones that filled your pathway - that lead you to this. If s/he makes comments or suggestions, that seem very direct, he is doing it for your own good.
Always do your best, during recovery. Of course, your best is going to change everyday - strictly depending on your mood. Under any circumstances, ALWAYS do your best. You will avoid self-judgement, relapsing, and self-harming.
If your psychologist puts you on an eating plan - don’t think that he is trying to “make you fat.” It is just to jumpstart your metabolism. If they ask you to surrender all your SH tools, do so.

Good luck, and congrats on your very difficult decision!