Assuming the man is Clark, maybe if he has a son he doesn't need to go back to New Krypton. A son with an Earth woman could free him from his Kryptonian marriage and his duties as a Kryptonian noble.
Another possibility: Superman is tested for fertility when Leigh-Anne claims Jesse is his son. He finds out that he is compatible with Earth women but that he's becoming sterile (maybe an effect of the repeated exposures to kryptonite) and just will be fertile for a short time.
Anyway... Woohoo! More Squid fics!
And let there be babies! They're too cute to resist.