But why is he so he'll bent in fucking the heroine?

He's the type of crazy ex that would extort her into being with him. Remember he still has the pictures of them together. However, he's not blackmailing her because he will then have to delete them in front of her. He can't do that because he likely jerks it to them. He wants her to feel dependent on him and to never get over him. She wants to just live a happy life in spite of her past, meaning that she really does love her husband. He can't get over her because he want absolute control over her in every way, shape, and form. Don't worry because later he pays the price.