You are absolutely correct.
You've done the right thing.
And you were 100% justified in doing it too.
Ignore the few posters who say otherwise; they're talking a load of shit.
They think a man should take agency and true consent away from two or more women, bring a child into the world with one of them... And it should be covered up??!!
For whose sake?
There's something wrong in the heads of these people.
Maybe they're betrayed wives who stayed and operate their marriage and life in ostrich mode, and blame the ow for having the gall to tell them Instead of blaming their "husband" for betraying them. You can't reason with such a lack of logic and integrity.
Other woman, who have usually at best been told a age old & effective script to get them to involve themselves with a man (he's not happy, his wife is a shrew, they're not a true couple anymore, he'll be leaving), or at worst been totally lied to & deceived as in your case; are supposed to slink.off and keep their mouths shut. While he fucks everybody over. Of they're angry, they're "vengeful". Listen, when women have sex and bond with a lying, future faking man who then throws them under a bus, and they realise they've been had; it's a type of fraud. And victims of fraud commonly get angry. That's even without the emotional and sexual element.
That does not change who the perpetrator of the fraud is. If you want to stay with a fraudster, stay .. stay but don't blame the victims of fraud for not staying quiet and crawling off and not bothering you with inconvenient facts.
Op is as justified as an ow could ever be to tell pertinent parties tell the truth. She's been totally deceived and has even been left with a child out of his gigantic deceit. He's even tried to blackmail and threaten and manipulative her in the worst way possible to force her silence too.
Fuck him. And if his partner would rather not know or is staying in spite of being told what sort of creature he is, more fool her.