I pay £450 towards household bills and food.. my own outgoings as well are a car, Petrol, my DDs clubs, clothes etc, my mobile phone so after that’s all paid I have about £150- £200 pm left. The mortgage on the flat is about £500
That's more than enough outgoings on an income of £800pm and I fail to see how anyone can't understand you won't be able to cover more bills. You don't earn enough.
Those banging on about you having a cushy number are just horrible. He's 'putting a roof over your head' as if you don't contribute a thing? You are his partner not an acquaintance. You're not sponging off him.
You're paying out over 1/2 your monthly income in bills and shopping. You're not costing him anything. + He's not paying for household food nor is he paying all the bills so he's doing ok isn't he?
I'd have thought he has savings, he has almost £2000pm left after paying mortgage. I wouldn't want to be with someone who is financially irresponsible. Those suggesting you've got it cushy and should move out (just like that 🙄) well then if you did you may not be that worse off depending on if you can claim Tax Credits, single person Council Tax discount etc. & Although you didn't mention it, you must get Child Benefit.
You are in a very vulnerable financial position yourself. Unmarried, name not on mortgage. You'd have been better off not moving in. As it is, you have so if you can stump up another £100 say, then all well and good but you won't be able to provide much more than that will you? It is what it is