In the end it was still his decision. He's a stupid heartless man who puts pride over love and killed two people he should have cherished for it (though one unborn).
What use will do revenge for a dead man who's cause of death were in the end his own wrongdoings. It would just serve self satisfication and be of use for some petty pride.
I'd curse the man, who was supossed to love me and my child and who was supposef to protect the two of us... ╮( ̄▽ ̄)╭
The princess is at fault too but in the end he wasn't directly forced to do it. I doubt the emperor would have killed him for admitting her being his lover but he'd lose a chance for revenge (which either way got taken by our dear state master ლ(´ڡ`ლ) ) and probs get on bad side of princess.
But it was still his decision (〜 ̄△ ̄)〜
Though just my opinion to curse the man ლ(´ڡ`ლ)
HAHA! SERVES YOU RIGHT BASTARD!
I hope those vengeful spirits of your girlfriend and her unborn child haunt you for the rest of your life until you are cursed to death and they are exorcized as you die so they can pass onto the next world instead of lingering.