After My Son Died My Husband Went Crazy by Davidmia

Story is complete as is. But is also a garbage ending. Not really any remorse for either of the villains, the husband even mentions the mistress in a positive way in his death note, knowing she killed his only child. The woman was fully aware of his marriage and child the entire time and chose to be the mistress and homewrecker, but the way this ends, it's no big deal and he's not really sorry that he wanted both of them.