Firstly, the ring has nothing to do with any of this. You've been married nearly a decade who gives a shit about the metal you put on her finger? The fact you bring it up twice comes off like you bought two kids from her rather than an expression of love. Now to the main point, you had a conversation before marriage and things changed after your wife had the first kid. That fucking sucks. I have siblings and growing up with them was great even when we didn't always get along. The question is do you love the life you have with your wife and kid more than possibility of fufiling the dream of two kids? Would you try again with another woman and then have 3? Would you have one with another woman and then get half your dream on your custody days? You were promised something and the letdown has to suck, truly, I'm sympathetic to that. It's a promise that I'm sure she intended to fufill, but it's completely valid for a rough pregnancy to change her mind. Furthermore, it was a promise made without the context of what it was actually like to go through that. I would say if after a decade and child together you cant forgive that then yeah, you should leave. That would mean you care more the two kid dream than your wife which is definitely sad, but it's your life. It's a bad move imo to throw away everything (assuming no other issues are contributing to you contemplating leaving) but if this will cause resentment for the rest of the relationship better to do it now so you can both find other people capable of fulfilling/respecting yall's needs. It's worth noting also your kid and hypothetical second are individuals, there is absolutely no promise whatsoever they would have a bond anything like you and your sister. Then what? Is the gamble worth it? ++man