I’m sorry it’s so difficult. Any variant if the blended family can be tough.
But aren’t you potentially just asking any potential new partner to be in a similar position to the one you are in now? I.e. with someone who already has a child with someone else, who might share custody. The exact details might not be the same (unplanned pregnancy, may sbehaving children) but the fuzzy lines and overlapping patterns of who’s related to who will be the same.
You say you want another child. What if your new partner wants two or more children and you only want another one? Will you be more or less accommodating than your current partner if your new partner longs for more than one child.
If you long for another child, would you feel it necessary at some point to accept a new partner who already has children but wants just one more? In which case, things have become even more complicated.
You need to be careful you’re not just putting someone else in your current unhappy space in your stead. You’d just be putting someone in your cage so you can escape it yourself. That often doesn’t work out well.
And I would be wary of pushing any blame onto your stepchildren. Whoever’s fault this situation is, if it is anyone’s fault, it’s really not their’s.
However difficult you are finding this set-up as an adult (who went into it with some choice, even if it went forward more rapidly than you planned) you can bet that they are finding it even more difficult as small children who had no say in the matter and much less understanding of the adult dynamics at play.
It might help to use your own unhappiness to have insight into how they are feeling and their behaviour. I’m not saying that will change the actual facts of the matter, but it might orientate you better to your step-children and make your situation bearable. How would you feel, if, in a few year’s time, your new partner was call your child difficult or badly behaved because they were unhappy with a complicated home life, or found it difficult to adjust to new step-siblings? Your future situation might not be that different from your current set-up if you go down this road, you might just have a slightly different role/position in it.
How will living apart from her father and step-siblings affect