I can't remember the title, anyone knows it?

It's about a demi-god, her God-father made 3 children which are the demi-gods but the 2 younger demi-god sinned. The blonde demi-god killed his lover because his lover fall out love & the youngest demi-god killed her son because she can't bear seeing her son suffering from a disease. And that's their sin.

The God-father cursed his two children to repeat their sin again & again.

Later on the oldest demi-god killed their God-father's mortal body because he cannot bear to see his sibling suffering & made his own world called earth. The male lead is atheist so he's the only one can kill the God-father.

That's all I can remember. Please help!