What's wrong with me?? HELP

ATTENTION: Slut Shamers gtfo.

So, I'm having some issues lately. I've been with my fiancee 3 years, and the sex is INCREDIBLE. He even spends like at least 15-20 minutes going down on me before. (We wants to make sure I have an orgasm before he does). And I'm all about sexy I realllllly am. But lately, I'll want to, and once we get started I just really want to stop. And I mean he's so sweet and understanding, that's not the problem. But I feel terrible because I know I live sex, especially with him, and I know for sure the spark isn't dead. So why do I get anxious to the point of nausea lately when I try? He's too sweet to ever say but I think I'm hurting his feelings.

UPDATE: I am in recovery from an eating disorder and have recently gotten back to a normal weight.