You're not responsible for dreams except if you did something during the day to cause you to dream it.
Seems like I read that in the Summa. Dreams lack willful intent, unless you into directed dreaming.
A bit of a problem, really, as the body wants a way to clean out the old sperm and thus increase fertility. No sex means wet dreams.
Mostly, you don't remember these dreams. Just have bad thoughts for a bit after you wake up.