For me the nightmares ended when I was no longer focusing on the CSA. Dreams are a way for the brain to process and sort information, so when the emotions, memories and need to deal with the CSA are part of the waking life that becomes the material that the brain needs to process during sleep. I think it can be a vicious cycle, too - when you think about during waking hours, it then becomes part of dream life, and when the dreams are disturbing it produces more 'fodder' to think about during the waking hours (which in turn feeds the nightmares again).
My nightmares about it didn't completely stop until I finished therapy, but towards the end they were infrequent. Dreams about it now are rare, and usually only occur when something has stirred up the issue for me during the day time.