I have ongoing mental health issues which he can find difficult. I'm also left to do the bulk of the house work/decorating and totally responsible for our cat.
Your b/f is insane to push an unwilling woman into conceiving a child for him.
You would be insane to comply.
You'd be left with ALL the work it entails, he would not support your MH (he finds it 'difficult' now ffs) - how are you going to feel, stuck at home with PND, a baby you did not want, & an unsupportive b/f?
Note that he's not offering marriage. You wouldn't even have any financial & legal protection if you went ahead with this insane plan.
I don't want to lose him
And he doesn't want you unless you provide him with a baby - a baby which he obviously will not step up for. He can't even look after a cat or do housework. He certainly won't step up to all the work & sacrifice a child entails.
As to not losing him - what are you going to do - keep stringing him along, while secretly taking contraception, just so he doesn't leave you?
He is perfectly reasonable to leave you. He wants a baby. You do not. You have not been straight with him.
What IS unreasonable is his behaviour outside of any babymaking wishes.
He doesn't support your MH, he reckons you are his domestic skivvy, & he can't even look after a cat.
Why on earth don't you want to lose him?
Do the decent thing for both of you & start telling the truth. No, you will not have a baby. Yes, that means you need to split up.
If the sexes were reversed here you would be getting a kicking from PP for the stringing-along for 2 years. It's unfair. I can understand why you did it - you are scared of being alone. But you might find that a change of circumstances & a commitment to looking after your newly single self as best as you can manage ends up being the silver lining your MH needs.
Right now, you are selling yourself the falsehood that you cannot manage without your b/f. This is bullshit, & look at the desperate behaviour that false belief has driven you to - you have been fibbing to your b/f for 2 years about having a baby with him. Instead of this relationship, invest in therapy for yourself, uncover what has driven you to throw in your lot with a man who can't even manage to look after a cat & expects you to do all his domestic drudgery.
You could come out of this stronger, more resilient & independent, & genuinely much happier.