One other thing... God created the whales, sea creatures and winged fowl before man, commanding those creatures to be fruitful and multiply, etc. Would those creatures be wrong or sinning if they had sex to reproduce? (Before Adam and eve even existed)
You must first prove that 'be fruitful and multiply' was about procreation in the first place. In other words, God could have simply made the creatures appear.
Think of how Jesus multiplied fish and bread. Did the bread have sex in order to multiply?