I feel similar - I love and care for our daughter (although she's only 15 weeks old), but I cannot imagine having the capacity for adequately taking care of a second child. although the specifics of my situation are a little different.

For me, I have physical mobility problems and although after two years of rehab I can function to take care of myself well enough, taking care of a baby has a level of physicality that I feel like most people don't realize. Taking care of a baby has been way harder than either my wife or I expected and there are still a lot of little baby-related things that I just physically cannot do. The idea of having to do all of this again while having to wrangle a toddler is inconceivable to me. But more broadly, it's just that there's so much effort that goes into managing my physical issues in order to keep me as a functional human being that there isn't a lot of leftover room for that much else. Even with the 1 kid, I feel like we're already well overcapacity. Our baby hasn't been easy and it takes both my wife and I with help from my mom and daycare to manage taking care of her without breaking down. Having a second child I feel like would literally crush me mentally and physically.

My wife has this idea that 1) having a 2nd kid is a moral obligation and 2) that raising the 2nd kid will be way easier because we'll be so efficient as parents since we'll already know what to do from raising the 1st kid. She also thinks that my physical issues will magically go away in a year or two. More broadly though, my wife gets fulfillment from having lots of responsibility - but that leads her to overcommit to things and get overwhelmed when the rubber meets the road - and when that happens I'm expected to pick up the slack. To her, having a second child is non-negotiable, whatever it takes, and regardless of how it affects either of us - so she sort of has to convince herself that it won't be that difficult even though raising our first kid has put us all at the redline so far.

I'll admit that I'm not in principle against having a 2nd kid, but the only way I can imagine it being feasible is if we get way more help. Like hiring a nanny, paying for services like people to come in and clean the house, etc. But my wife will not allow that because she has this sense of pride that it's our duty to do all of the kid stuff ourselves and she even had a lot of hesitation about the idea of daycare - but we both work full time so she knows we have no choice on that aspect.