He knows that he made a mistake and so does Tess. She finds herself absolutely hopeless in this situation and kills Alec because she believes that he is guilty for all the bad things that have happened to her. By killing him she kills her past and nightmare. She leaves with Alec but she fully does not realise what she has done or she does not want to realise it because the only thing she desires for is to be with her beloved husband and to feel his renewed love to her. They are spending several days together hiding before the police and I think that Tess has never ever been so happy. Finally she has what she has always desired for. But as I have mentioned before Thomas Hardy always changes the situation when it seems that the main protagonist could be happy forever. Tess is arrested and sentenced to death but her love remains in Alec’s memories.
The fate plays an important role in our lives but the question is: “Is it true that our lives are already planned and that we have no power to change them? What if Tess’s father has not been told that he comes from the family of the d’Urbervilles? Would she have been suffering more or not? Would she have met his beloved Angel? These and many other questions will never be answered. But does it really matter?.