Alpha Clark and omega Bruce try for a baby. Their pack is happy, and thriving, so Bruce brings it up to Clark hesitantly, after a lot of internal debate, and talking to his kids—Damian and Kon especially—to see if they were open to the idea of another sibling. Not too much information, just putting out feelers, and getting a positive response.
Clark says yes. But not for the right reasons. He is terrified at the idea of being a father. (Let's just go with Lois and Clark never had Jon when they were married.) He has Bruce's kids, and he has Kon, but their relationship is still rocky (ik that's just the YJ cartoon but shh), and the idea of a baby terrifies him. That's eighteen years he has to mess up, not to mention everything after that. He can barely handle his teenage son, let alone a baby.
So Clark keeps it a secret that Kryptonians don't procreate the same way humans do. Well, he does, but there's another stage he just... doesn't allow to happen. So they try, and Clark convinces himself he'll get used to the idea before Bruce has time to realise anything is wrong.
And he does. Slowly, he realises Bruce is just as nervous, he's messed up so many times with his own kids, but he believes in him and Clark being able to do it together, which gives Clark the confidence to finally be okay with the idea.
But it's too late. It's been months. Clark had watched Bruce start to test his fertility, going to Leslie for checkups to see if his damage from Batman was too much, consumed by guilt, but hadn't noticed Bruce go to the Fortress.
Didn't notice until he came home from work and found Bruce curled up in his nest, eyes red. Not until he tried to enter, to go to his mate and comfort him, and Bruce growled as soon as he had a foot in the nest. Growled at Clark, who's had a blanket invitation into his nest from before they even started courting.
Clark knew, instantly, that Bruce found out. They were there for ages, him sat outside the nest, not breaching the boundary, begging for forgiveness, he's ready now, he promises, he's sorry for lying. Bruce, who has spent months berating himself for being a bad omega, who has struggled from the very beginning to feel worthy of Clark, believing Superman deserved a better omega, one that didn't need to physically put in the work to listen to their instincts. Who has felt guilty that he couldn't produce a pup for his mate, who was held and comforted by Clark, given false platitudes of 'it will take time' or 'it doesn't happen right away for everyone', when he knew the reason behind it the whole time.
Eventually, Bruce orders Clark out in a whisper, and he leaves. Leaves their bedroom, and sleeps outside in the hallway, listening to Bruce try not to cry, and whine even in his sleep, horrified at what he did to his omega. He didn't realise how much he'd upset Bruce, and now it's too late.
Now, he's watching Bruce barely able to be near him, watching him try and put an act on for the kids, because his mate is so good, and so kind, and doesn't want to discredit Clark in their children's eyes. Watching the kids stare at them, examine them, spy on them, trying to figure out what has happened, why Clark is sleeping in a guest room. Watches as his family fractures— his mate fractures, knowing it's his fault, unable to stop it.
He goes to Bruce, eventually, tells him he doesn't mind, please, tell the kids what Clark did, don't isolate himself from them. Bruce just stares. "Do you really think," he says, "that I want my children to know what a fool you've made of me?"
"Our children," Clark corrects, firm.
"Mine. You have made your stance on having children perfectly clear, Clark."
Anyway! Don't know how it ends, but this wouldn't leave my head. Also, I know there's an anon that wanted alpha clark/omega bruce but this felt a bit heavy for that ask, I'm give you something Iighter, promise!
