You are very right in what you are saying. We made a mistake by not being specific enough about what safe sex meant to us and that is a mistake we haven't made or won't make again. Being upfront and totally honest is the best way to go.
I ended up getting pregnant that night (birth control failure) so I guess what happened was for a damn good reason.
I go to sleep every night knowing who fathered my child and if things had went different that eve, I would always be wondering.