I think you need a clear plan so in your head you know you are making progress.
You need to look after your mental and physical health as a priority. Keep the doctors appointment, but also nourish your body with the right foods. I wouldn’t start off on the injections, just cut out the takeaways and put the money into a divorce fund if you can or use it for therapy. I wouldn’t start off find something that helps with your stress as an outlet, walking, yoga, tai chi, qui gong, a class maybe where you might have an escape from the house and meet people. Do something to make yourself look good, a mini makeover, nails, haircut some make up to act as your war paint.
You need to look at your financial situation. See if you can increase your hours at work and don’t pay another bill. Don’t tell your DH if you can avoid it and if you can’t refuse to had over any more money. I personally wouldn’t tell him why, potentially saying you want to save for a car of your own or emergency savings or putting more into your pension. I would open an account that he had no knowledge of and save as much as I could. No doubt he has savings of his own in his name. I seem to recall at least one poster on here getting cash back every time she shopped in a supermarket and saving that money so her husband didn’t know.
Practically you need to find out where you stand. How much do you know about your finances as a couple? Maybe look at doing a statement of affairs from money saving expert where you list your family incomings and outgoings, debts and assets and photograph anything that looks important, like savings statements, credit card debt, mortgage balance, pension summary etc. I would also look at rightmove to see if you can workout a ballpark figure for the house if owned. Then I would see a solicitor to find out where I stand.
Do you have anywhere you and the dc could go to? If not you might be stuck in the house for a while if he won’t leave. You already have separate bedrooms so along with the strictly no sexual activity, I would try and be civil to him to co habit as civilly as possible until you are ready to tell him your plans.
It sounds like the house is in a mess and I might be different to some other posters but I think it might make you feel better if it wasn’t too bad and it isn’t great for the dc either so I would get help from them and get it sorted. I would think of this as exercise to help you burn calories and also if you can discretely sell things, it’s money to help your fuck off fund. If you sell the house it will also help.
You also need to get as much support around you as you can. Do you have any relatives or friends you can talk to in confidence? Would work be supportive? Keep posting on here but if you can get some real life support then fantastic, as others have mentioned there are charities than might be helpful.
Life is too short to be so unhappy and you will need to get your courage up but it will be worth it when he is gone and you are settled in your own place. You need to become your own cheerleader and ask yourself what can I do today to improve things. It might be a huge step, it might be shaving your legs or changing your bedding. But ask yourself every day, what can I do to make me feel good?
If you do what support there are weight loss support sub sections on here for all sorts of weight loss methods, like wise financial support on here or MSE.