There is a Buddhist meditation called Metta Meditation, which I think might help. But I also think it would be extremely difficult to direct compassion toward this "man" -- that's the direction the meditation would lead in.

The trick (maybe) is to understand that this person is deeply flawed and might be incapable of experiencing the joy of a true, loving connection with someone. How can anyone do what he did without suffering in the process?

Perhaps it might also be difficult to direct compassion to yourself, which is another aspect of the meditation. But I hope you'll try that part of it at least.