Assalamualaikum ustadh May Allah preserve you I struggle with thinking and writing very dark scenarios of abuse and violence and many horrible things . I assume they are sinful to write. How to stop falling into this. I feel ashamed, afraid of men , as if I'm in an actual horrible relationship etc.

May Allah protect you and cure you. The thoughts themselves are not held against you. The Prophet ﷺ said: إن الله تجاوز عن أمتي ما حدثت به أنفسها ما لم تعمل أو تكلم Meaning: Allah has pardoned for my Ummah what their souls tell them, as long as they do not act upon it or speak of it (agreed upon, al-Bukhari and Muslim). What stays inside is forgiven, and the matter only counts against a person when it is spoken, written down or acted upon, as Imam Ibn Baz explained. So stop writing these scenarios. When the thoughts come, say A'udhu billahi minash-shaytanir-rajim, do not indulge them in any way, shape or form, and occupy yourself with something that benefits you.