I am sorry for your experience and the presence of this individual in the seminary.
That said, you must move on. Get counseling if you haven’t received it.
Drop it and hope that he won’t affect others the same way.
I experienced PTSD after what was for me a traumatic delivery. I hated my OB and wanted to kill her. I got counseling. This was before PTSD was recognized as a distinct entity. I myself recognized my problem by reading in Time magazine about what Vietnam veterans were going through. It took a long time, years, for my feelings to fade. Now I recognize it for what it was. I suspect that you went through far worse, but feel that counseling is essential, especially at it has already been several years.
Another thought: which others mentioned.
Why didn’t your cousin priest come forward? After all, he’s a disinterested observer. He’s a grown man and a priest. He has no axe to grind.
If your cousin is still alive and well (sorry…) and still interested, he can still come forward, citing the lack of response to your previous attempts, perhaps interpreted as sour grapes by an embittered girl.
I happen to think that people don’t fundamentally change. I think that abusers remain abusers. I would never tolerate someone who yelled at me or anyone else, and it’s not tolerated in my workplace, and increasingly, not tolerated at all (vis. recent attempts to control school bullying). It may be covered up but eventually will erupt.