Cos she knows shes broken up a family? Left 2 small dc with no dad?
SHE hasn't broken up a family.
Your husband flirted with her, arranged to meet her at a mates house and fucked her. All planned while you were in hospital.
HE broke up your family.
HE only told you because she mentioned the police.
YOU have reserved your venom and vitriol for her because it's easier than laying the blame where it lies - at your husbands feet.
She was after him for ages you say? Sent him nudes you say? So instead of behaving how he would if he gave a shiny shit about his family, he indulged this, shagged her and THEN (after fucking her) told her she was out of a job!!
This kind of man hates women. He shows disdain for them.
He showed disdain for you when he planned to shagged an 18 year old behind your back while you were in hospital and went through with it.
He showed disdain for her when he shagged her then told her she has lost her job.
From the way you're talking I don't buy that you've kicked him out and told him it's over for good between you, but I hope I'm wrong.