I know exactly how you feel. My so once lost about 20 pounds and I felt like my insides were being twisted inside out. It doesn't help that you know it's an irrational response, and you truly just want to support them in what will make them happy and be best for them. In my case she gained it all back and more very quickly so it wasn't a big deal, but if it happened again I would need to find some way to deal with it.

You could try looking into seeing if a psychotherapist or even clinical hypnotherapist could help. You probably would need to try a few things to find something that helps, given how deeply this is engrained in us.
Many feeders also have latent feedee tendencies too. If this happens to be the case for you, then you could also explore a switching of roles to scratch that itch, if he's open to it.

Every year pornhub posts stats about usage and popularity of categories etc... Over the past year. You could take a look at that for some insights into the relative popularity of bbws, amongst other things.