Fortunately, the title is not what is being discussed. Therefor has a different treatment. I would use "He hated her; therefore he stopped speaking to her." The semicolon indicates a longer pause than a comma. If faced with the first, "He hated her, and therefore stopped speaking to her." I would accept it. The pause is not needed. Note, however, that I removed "he".
I'm sorry if I was not clear. The first is acceptable with a semi-colon. The second is edited by removing the second occurrence of "he"; and it can use instead a comma.