How does once loving someone so dearly, going through the trouble of marrying him/her, degenerate into Hate? Hate to the extent of getting physical and killing is involved?

The question has two answers.

1 They never loved each other or
2 The once loved each other but now they started seeing the faults of one another. The once had a heart that easily forgives and a eye that easily over look faults. But those eyes and hearts has being replaced by hatred and pride.

Things will never go when there is true love. Love and hatred can never dwell together.

Thanks @ceepee, that's my view