It's good that they're trying to be civilized, but if she hadn't been pregnant the marriage would have been annulled, and I've never seen a marriage work because of an upcoming baby. Although both are now reeling from all the emotions the fact remains that having a baby cannot keep a broken relationship intact.
The true measure of a person is how they treat you when you're at your lowest (in Clark's case sick and needing an operation to live), and that's when Lois knowingly treated Clark like a pitiable pest. She made it obvious that she wants him to live, just not with her. Their having a baby, no matter how welcome, cannot alter that unchangeable reality.
I can see a HEA here: they divorce and stay friends. Are they supposed to stay together for the baby's sake? Eventually one or the other is going to want to experience real love in his or her life, not just share the bond of legalized parenting. They don't need to be married for that.
