My married co-worker got one of his subordinates pregnant. No one said anything to upper management cause the woman does not want to pursue any claims (her own choice). Plus, everyone know about it, including management, and they didn't pursue anything either

Now my co-worker may not get a job with a different company because the owner found out about it through a third party.

Can the owner not hire my co-worker cause he got a girl pregnant? Can my co-worker go after the people who told the owner this, and other damaging personal stuff, that has never affected his work (except the knocking up of the woman)? Is that considered libel?

It would be considered libel if it wasn't true.

This event may not have affected his work but it does show an incredible lack of judgement on his part and that he holds no loyalty to the person he married.

He also exposed his current workplace to a potential sexual harassment case since he got himself involved with a subordinate. Sure, she is okay with him now - but that can change at a moments notice.

I can see why the potential employer wants nothing to do with him.