Feeling guilty. Have i gone too far?

I just need some advice I've been with my (36f) partner (43m)for nearly 5 years. He has a daughter (10). We get on really well and she does love me. I love her. We have just bought a house.

Since buying it We have argued a lot. I've put my savings into the house and covered the deposit. I also got a second job to cover solicitor fees. He's really busy with his job that can have him up on call

When we started seeing each other, we had the chat where I said I want my own children. He said he wanted more.

Now fast forward to now. We've brought up having children in front of his daughter. She started crying and saying she doesn't want that. She is my partner's world. I think I have been resenting her because of it. And when she's sassy towards me, I usually let it slip, but recently I've snapped at her and it's caused an argument.

I work from home and in the new house we have an outside shed that is going to be my office. I'm currently working from the kitchen table, which causes tension as my job is quite full on, so could easily stay working later. When we were talking about getting the office ready, SD wants her own desk in there for her natural history bits. This caused me to get frustrated but I didn't say anything. I'm largely to blame for my terrible communication, it stems from bad past relationships so I'm terrified ill say the wrong thing and this one will crumble.

It's all come to a head tonight, we've had another argument around how I'm snappy etc. But my partner is also snappy and he hasn't admitted why. So I feel like the problem. Apparently he feels like he can't do anything right either.

Our private time has been suffering as I have come off contraception, not to get pregnant but because it was screwing with me, I take my temp every morning. Tonight he said, he didnt see the point of my doing this, it wakes him up and it's not working. He also revealed he now does not get pleasure from s** because he has to wear protection. The point of me doing my temp was to track my non fertile days.

Long story short as I'm waffling. I finally told him about the baby thing and the resentment, he revealed he's cross at me because of how short I am with his daughter. He told me he loved me and was sorry my life hasn't been the way I imagined and that he wouldn't blame me for leaving.

We've both admitted to a wider problem, but i don't want this to end, I love him and his daughter. How do I fix this? How do I stop feeling so alone? I feel so guilty. Am I wallowing? I am so lost

Edit just to clarify: SD did get her space in the office, I doubt it'll be used at all. She's a good kid and a pleasant one. She does always get her way though. Her opinion is always asked for by her dad. While I want her to be happy, I ultimately won't consider her opinion to be the way forward. Her dad and her are very close. He refers to them both as "we". Im an add on. Maybe more enlightenment as to why I feel resentful. Which i fully admit is not healthy.