ahh The one(s) that got away.. It just wasn't meant to be.
I suggest producing children at a distance, you can still visit them all you want; it's all the fun without the responsibility.
If you can sneak in under the radar and copulate with another sims Wife or Partner they are often none the wiser and will raise said resulting children for you, feel free to repeat at your leisure. My current heir has several children being raised by other families and it's been nothing but daisies for every sim involved.