Like other German work camps where Nazi officials were placed in charge of Jewish inmates, Amon Goeth oversaw the Plaszow camp with ruthless, heartless, discipline and unrealistic expectations. His disregard for any human whom he did deem worthy of respect or life was appalling and inhumane. He was a cruel, narcissistic authoritarian who had no problem killing a Jew for the slightest reason. As Goeth enjoyed demanding obedience and respect from the inmates, he became obsessed with power.
Goeth personally chose the Jews at the camp to work in his home, and he chose Helen Hirsch to be his maid. Clearly, Goeth loathed Jews and all they represented; however, Helen caught his eye. He was attracted to her, but he fought his feelings of attraction as he despised all Jews, including Helen. While he did want to kiss her, his prejudice and unbridled hatred of Jews challenged his attraction. You can expound on how his feelings for Helen made Goeth even angrier, as he could not rationalize or support such feelings.
Also, consider the fact that for Goeth and other Nazi officials, showing any kind of affection (even if it was a stolen kiss) towards a Jew would be a sign of weakness. After all, Goeth stepped on, beat, shot, and murdered Jews for no reason; he viewed them as animals or sub-human beings. He could not defend being attracted to one, as he thought himself superior to all Jews. He wanted to project superiority and strength at all times. Would he be considered less of a Nazi if he spared Helen and was with her? As he was a man used to always getting his own way, he became obsessed with her. At times, Helen was afraid of Goeth and at other times, she appeared ambivalent toward him, and that bothered him. Helen represented an unmet desire and unquenchable lust that Goeth could not settle.