1. Kids raised by splitted parents can be as fine as others. Ofc some can be messed up, but so can be those with parents together. The problem comes mostly from bad parents not if they are still together or not.
2. You get kids, then 18 years later they leave the nest, and so they are not a reason for their parents to stay together anymore.
3. Parents who stood together because of kids usually lead to awful families. Everytime I saw such situation, it was a disaster.
4. You can still marry, I am btw. But even if I hope it will last forever, I'm not naive enough to not consider the possibility it might end one day. And that's a good thing, as it keep your relation still challenging.