Many men (like me) find fat women to be very attractive, and many fat women enjoy stable and loving relationships. If you’re approaching every potential partner with the attitude that you’re unattractive and they couldn’t possibly be interested in you, that will have an effect.
You don’t deserve to be insulted when you’re out shopping, but there’s not much you can do about that other than telling rude people to mind their own business.
There are many dating sites that cater to fat women, so you may want to look into that.