What do I do ..?

Hey I'm in a relationship with a Guy and we've been together for almost 9 months exactly, I told him I'm on a diet and he seemed supportive or it and was helping me count my calories and everything and I told him I weighed 125 lbs. (I am 5'4)  At the end of the day I finally told I wanted to go to 100 lbs and how idk what I'll do when I do reach that weight (like what eating habits I will do) he immediately told me I was retarted , I'll look so anorexic, I will look terrible and stuff like that.. It immediately made me feel TERRIBLE. I don't want him to not like the way I look but I want to reach this goal to just be confident.. I feel like I can't do both and I love him so much and i feel like I can't do both. He keeps asking what is wrong but idk what to say   
Please help me:(