Any woman who gets involved with a man who she knows to have a wife and child, whatever lies he spins to get her legs apart, is as guilty as he is.
Never believe the bullshit, however attractive and seductive it might seem. It's a well-known path.
And men who feel they're not getting the sex they think is their right, despite the fact the wife may be heavily pregnant and looking after their toddler, will tell those lies with zero conscience, as so many accounts here will confirm.
I wonder if she gave him an 'I don't want to be alone at Christmas' ultimatum, he turned her down, maybe ended it - and this is both her revenge on him and a knife twist for the OP for having won this 'prize'?
Or if she genuinely believed the married man's lying program he was running - until the pregnancy news came as a nasty dose of reality and this is a late surge of guilt and remorse?
It will be interesting when they have to keep working together.
Whatever, it's unlikely having delivered this domestic, emotional and financial wrecking ball into his cushy set up that he'd be going to her with much joy.
And even if he does, OP please beware the Mr Nice step on the cycle. Probably encouraged by his family who risk losing the grandchildren, or the soured collapse of the affair.
'I'm sorry, I made a mistake, it won't ever happen again', tears, self prostration for forgiveness, presents, promises, pushing all your buttons. It's a mask.
Because if you accept and forgive - he will do it again. Because he'll know you'll let him.
Your No will reveal more of his true nature, which will shock you.
Stay strong, OP, with your brilliant family, and lovely baby here soon.