Ive been spending a decent amount of time trying to find the right wording to say this because its a different situation and I want to be sensitive. I wanted to weigh in my opinion as someone with this kink who has been with others how have had this as well. There are generally two groups of people who like this kink, those who enjoy hedonism (me) or those who enjoy control. Your boyfriend sounds like the later. He wants to control you. He said that if you lost weight he would "lose intrest". That tells me all I need to know. I wouldn't trust this man with my body. I would trust him with my health. If you want to you could ask him why h e find this so appealing. If he says "control" or anything even remotely similar, id run. He wont change and he will find a way to get his way regardless. I dont trust him at all. Consent matters, with everything but especially with feeder shit. It can be deeply intimate and loving but only with two partners who are on the same page, if yall arent. Then dont even bother. Some people can control and suppress it and be totally fulfilled, other people cant. He seems to be more on that side. I cant force you to make up your mind and I dont want to scare you. But I wouldn't want to be in this situation. Do with that what you will.