Will Allah hold me accountable if I cut ties with my family, who did not defend me after I was sexually harassed, but rather continued their relationship with the aggressor for their own personal interests, and accused me of being in the wrong?

If your family knew about a man harassing you and did not ward off his harm from you, they are indeed in error. However, this does not in any way justify severing ties with them, especially your parents; this is based on the Almighty’s saying: "And your Lord has decreed that you worship none but Him. And to parents, show goodness." [Quran 17:23] And based on the saying of Ibn Abbas: "There is no Muslim who has two Muslim parents, and he serves them dutifully in the morning, except that Allah opens for him two doors… And if he angers one of them, Allah will not be pleased with him until that parent is pleased with him." It was asked: "Even if they wronged him?" He said: "Even if they wronged him." Therefore, it is obligatory to maintain ties with parents and siblings in a way that is customarily considered maintaining ties, and to avoid cutting off relations and estrangement.