You're paying someone to abuse you?

At least you are being honest with BF. I respect that.

To be fair, it might have been better to tell him about her before you embarked on this journey with her... at least, that way, you could have talked it through openly and honestly with him.

Does he have a full understanding of your submissive side and the fact that the control calms you??? Sometimes, that can help to bring someone over to "The Dark Side".

Just keep it healthy... that "calorie budget" thing doesn't particularly thrill me - especially when I know that you recently more than halved what you need to eat to be healthy. Maybe something like Slimming World might help you, too - at least, that way, you'll have people to watch over you and help to make sure that you are safe.

The meetings with your mistress sound like an interesting combination of therapy, self-help, and kink. Well played!

It sounds like you’re pretty sure about your decision. I hope your boyfriend takes it well. I’m sure you have thought about it a lot and will explain to him in a sensitive way what’s been going on. This must be difficult for you. But it sounds like you are making changes in your life that will set you both free, so kudos for that.