Basically I've had an issue with how my partner parents (or doesn't parent) his daughter. My honest opinion is that we moved in too quickly and now i'm forced into a situation i don't want to be part of. 
We haven't had his daughter ( 3 years old) for 5 weeks as she's been poorly and then he was poorly (obviously can't be too careful with the whole coronavirus). Bearing in mind her biological mother is working from home and her excuse for never getting her in a routine was her work and finishing at 8pm. So we had her for the first time again last night and my 5 year old goes to bed at 7, with a DVD and then is asleep by 8:30. So as both the kids cant go to bed at the same time as they get up to play or chat all night so basically when we have his daughter she goes to bed at 7, we wait for her to fall asleep and then we put my daughter to bed who understands on the weekends we have his daughter that she can't watch a DVD and goes straight to sleep. We attempted to put his daughter to bed last night at 8 (and only because i mentioned that it's keeping my daughter up aswell as she has to wait). He tried to argue that she's not tired which my argument is that the kids don't tell us when they go to bed, we tell them. He lied when we moved in together and said she slept through and in almost 2 years, its been a handful of times, which isn't fair on my daughter being woken up as they have to share a room. So basically 9:30 and she's still kicking off saying she wants to go to mummys house - i told him not to take it to heart and it's only because he's making her so something she doesn't want to do. My daughter used to do the same when i told her off and she'd ask for her daddy. So they facetime her mum, who asks if we've given her milk (she kept being sick on it and the doctor advised not to give it to her so why the hell has this thick idiot been giving it to her, she's 3 and i put my foot down that im sick of cleaning up milky sick all the time when she needs comforting in the night and not another bottle - and it was in a baby bottle at AGE 3!). Her mum then says we're trying to put her to bed toom early. Its fucking 9pm and she's still kicking off. Me and my partner have the perfect relationship and the only thing we ever argue about is his daughter and her behaviour. I've held in how i feel about her behaviour for almost 2 years but its getting to the point where i literally just cant be bothered anymore. He's said i make him feel like i dont want her here (i don't when its a kick off and a fight just to simply get her to bed). Her behaviour in general is disgusting and the way she talks is 'I WANT THAT.' And how whe speaks to my daughter is shocking. As a single parent since i split with my daughters dad, i've worked so hard to make my daughter polite, well behaved and in a good routine. Then i still have to deal with someone elses spawn of satan, so all my work is for nothing. The last weekend we had her, my partner was exhausted and he'd only had her for 2 days. I look forward to Sunday when she goes back to her mums. I want to disengage and let him get on with it but i don't want to be a couple who doesn't help each other out when needed. But i literally cannot stand his child. They way she speaks, the way she acts is just everything I didn't want my child to be, yet im now dealing with his child being like it. She kicks off over everything, and his excuse is always she's tired - or have your accepted that this is actually her personality? And you're constantly making excuses for it instead of actively dealing with it? I don't know whether to end things but he is literally everything i want, as they're a package and i need to accept them both even when i don't want to