Yes, I think there's a bunch of things going on here.
Co-sleeping is only a problem if it's stopping you from sleeping.
Nappies - meh. Dummies - meh.
The eating thing, has he always been thin? Or is he losing weight? It's a hard age for food, and an easy area to fall into battlefield mentality, but you can't really force a three-year-old to eat. I know it's hard to stick to your guns when you're worried about his weight, so maybe take him to see a HV or whatever's appropriate for his age, see if they're concerned about his weight, and if not, let that one go. Toddlers will not, WILL not, let themselves starve to death voluntarily. If he won't eat much, he won't eat much. Decide how much effort you want to put into cooking special meals and providing alternatives for your own sanity, and then stick to that. And give him a multivitamin for peace of mind.
As for going back to work and filing for divorce and all of that:
Why not go back to work? You'll get a break, you'll feel like you've recovered some identity (not that all women lose identity when at home, obviously, but you sound like you've lost yourself, and that no-one is giving you any positive feedback, and if you're defining yourself as Parent and yet feeling like a bad parent, it can't be good), and as a bonus you might find that daycare helps get your son into a routine. Even part-time. Is that a possibility for you, because it sounds to me like it would be positive all round.
And you need to sit down with your husband and have some of this out. It's simply not on that he gets to decide to abdicate from the position of Dad just because it's "too hard", leaving you to do everything. Set some family rules, if you can; everyone is home for a shared dinner at least 3 times a week, the family has a shared outing every Sunday, that sort of thing.
Once you've got a bit of confidence back in yourself, you might find it easier to lay down some boundaries around bedtime and bathtime. At the moment you sound like you've got absolutely no support and absolutely no self confidence.