It's highly, HIGHLY unlikely that you'll get pregnant this way. Sperm just doesn't survive outside the human body for very long, so unless his penis is actually inside your vagina when he has these wet dreams you're probably taking the EC unnecessarily. I wouldn't say you're abusing it, however, as it's not your only/intentional form of birth control. Sleeping with underwear or pants on is probably a cheaper way to reassure yourself you aren't going to get pregnant, though!