Clark and Bruce have been dating for a long while; they are even fiancés now! But planning a wedding takes so much time, not to mention the league business and world-saving. One day, Clark gets stuck in a time loop or is off-world, lost galaxies away. No one really knows where he is.
But when he returns, everything isn't the same. 1) It's been years; Superman is a long-lost legend. 2) He was so exhausted and under so many different shit that hit him, that left him kinda depowered (or fully). 3) Everyone he knows is, I don't know, wiser, different, older. But the last thing, "4," is the most devastating thing he learns from being back (probably from a billboard):
Bruce has a lot of kids, with the eldest being 17. They all look identical to him, so he probably got over Clark and moved on with his life, and now has a happy family. He probably found someone. And Clark should be happy for him. He learns it's been over a decade (oh, so B adopted some), so it's expected for B not to wait for him. And Supes is kind of presumed dead. He doesn't contact JL or B in this state because what is there even to tell when he doesn't even have powers? So unless he shows up at their jobs(civilians), they have no way to communicate. He doesn't have any use in heroism unless he wants to dress up as what? A chicken? And be a vigilante as well. All he has to worry about is how to get a job or an apartment or something because for most of his life he was with B. He can't just show up and say, "Oh, hiii! Yeah, it's me, Bruce, your ex fiancée, probably, haha. I'm back! By the way, can you give me a place to stay? I'm homeless beacuse, yk we used to live together. Also, I know you have kids and moved on, haha, which is great for you! Really happy for you. Just give me a bed for a while." He has some dignity left, and who knows, he doesn't want to mess up anyone's life right now (because what if it isn't Alfred or Bruce who opens the door, but whatever partner he has now? Well, that's awkward). Plus, he has his own problems to worry about. He'll probably go to homeless shelters. Oh god, he wished he had money to buy a train ticket to go to his Ma and Pa in Kansas. All those years must be painful for them.
Expect that whatever brought Clark back made some dimensional problems or a void, so now the whole JL is trying to guess what caused this and what it is. And they are kinda paranoid freaks now, so Bruce takes all of his kids to Smallville to their grandparents, the Kents, because whatever happened to Clark is still a sore topic and no one wants anyone to vanish ever again. In the end, they do find what fell out of the dimensional hole in a shelter, and that thing currently has crusts all over its face, also some facial hair, its hair is messy, eyebags under its eyes, and they guess that thing was trying to go to sleep, but what stands out the most is the fact that it specifically looks like Superman.
Does B beat the shit out of him? Yes, he does.(jk) He also cries a lot. He doesn't even care who sees him like this. That was his lost fiancée in front of him.
I still have no idea how to conceive Damian because I love Talia to heart like, go, girlboss! Idk why, but it rubs me the wrong way to think, "Yeah, he had a fiancée, but he's kind of gone now, and no one knows if he's alive or not. No one knows where he is, and there's no trace of him, so I guess he can have sex with Talia and be in a relationship. But then what? They realize that being together isn't really for them, so they break off whatever they had, but Talia later finds out she's pregnant, and they agree to co-parent?" Like ughhhhh idk what to dooooo here. God, i hate canon and fanon. And i love babian, thats so cute, so ig the only logical would be that. Also, Clark uses free computers from the library to find out what has happened while he was gone (mostly checking Bruce's personal life; it wasn't that they were public back then, so no one knows about a fiancée being gone), but he doesn't have it in him to go back to the manor. He will eventually, but right now he wants peace and to figure out what he has to do now that he's just as mortal as everyone else.