This was originally from the YJ anon meme. It's very reminiscent of miscarriage, so you may want to avoid it. I have not watched past Image, so this will ignore any episodes beyond that.
He's just gotten so tired of it all.
Clark was the last of his kind...
Except he wasn't.
There was Chris, Ben, Jamie, Callie, Heide... and eventually he just got tired of it all.
It was always hard, at first. He always tried to keep them out of sight, after Chris. Chris lasted barely a day. It had been such a lift, to not be alone anymore, to know he could pass on everything to someone, to know that someone else might understand.
And then there'd been Ben, and Clark had thought that Ben would survive. Surely, Chris had just been... just had a slight defect. Ben would survive, right?
By the time he'd found Heide, Clark had stopped expecting the clones would survive. He always hoped. But slowly, his own private cemetery filled up.
So when he arrived at Cadmus and saw his own face staring back at him (for the eighteenth time, plus five girls and two that hadn't... hadn't turned out quite identical) Clark couldn't deal with it.
He couldn't bury another child.
He let the clone join the team, and he tried not to look at him, because maybe if he didn't look at him he could pretend he hadn't seen that very same face staring up at him from a coffin eighteen times before (plus five girls and two that hadn't turned out quite identical).
The months wore on.
This was the longest a clone had ever lasted.
Every time he saw his face... every time he saw Conner (he'd named all the others why hadn't he named Conner, taken him in, why hadn't he), his heart leapt and then plunged to its death once again, because if he allowed himself to hope he'd find himself facing another burial.
And Clark couldn't bury another child.
He'd buried twenty five children.
Clark Kent wasn't losing this one, even if that meant not having him at all.