וַיֵּ֨צֶר לְאַמְנ֜וֹן לְהִתְחַלּ֗וֹת בַּֽעֲבוּר֙ תָּמָ֣ר אֲחֹת֔וֹ כִּ֥י בְתוּלָ֖ה הִ֑יא וַיִּפָּלֵא֙ בְּעֵינֵ֣י אַמְנ֔וֹן לַעֲשׂ֥וֹת לָ֖הּ מְאֽוּמָה׃
And Amnon was so distressed that he fell sick because of his sister Tamar; for she was a virgin; and it seemed hard to Amnon to do any thing unto her.
Read Kabbalistic (mystical) interpretations of II Samuel 13:2: Zohar and classical Jewish mystical sources, free online.