Insecurity issues

I’ve always been on the thin side but having two kids made me gain a little weight. The weight that I gained I absolutely loved. I loved everything about myself. My confidence was up, my head was even held higher. After having a mental breakdown I went from 165 to 116 in just 1 month. I can’t seem to get the weight back up. But if I was self conscious about my body before then you can only imagine what I feel now. 7/10 Times i don’t want to have sex or be bothered by my S.O. Yet he still tells me I’m beautiful but I don’t feel it. I believe he means it but I don’t want him to feel like I don’t want him. It’s literally an “ it’s not you, it’s me case”. What do I do?