I'm obese with poor mental health and no job.
plenty of people fit this description, yet find relationships where they aren't used for sex and insulted in the process.
i'd suggest working on liking yourself, and ditching this guy. i'm not going to tell you to hit the gym and start posting in
r/progresspics
(though that's worth a look, it's a super awesome sub) if you aren't inclined to do such a thing, but i will say that the working on yourself part is very mental, and you don't have to be a size 4, or 14, or even 24, to be worthwhile as a human being.
are you good at anything? passionate about something? if so, explore those things. grow them. respect yourself for them. are you kind to children and animals and old people? are you gracious with strangers? are you good at listening to people's problems? there are a million ways to find value in yourself and explore that value that have fuckall to do with how your body looks and whether or not you have a job. grow those things, nurture them, realize you're worth something, and when you do, you'll realize
he's
the one who isn't a catch here - not you.
in short, though, no, you shouldn't settle for this shit. some guy who calls you 'fat ass,' no. only mouthbreathing fucksticks use that as a term of endearment, and no one with a sense of self would view it as anything other than the belittling insult it is.
so work on yourself. mentally, not physically. do the latter too, if inclined, but the former is the important part.