Maybe this has been said but I think you should evaluate what MARRIAGE is, God made the first union right from there on in every marriage at least in most cultures was only considered real when it was consumated.
So whats the real marriage the ceramony or the wedding night?Every sexual relationship a person enters into is a sort of marrital union in my mind weather its for one night or 50 years.God blessed that first marriage since then who knows what marriages he considers legit and what ones he doesnt .dont get bogged down on trying to rationalize it. God knows you to the core of your being and intentions matter So if your feelings are sincere and your intentions are good with this girl why wouldnt God bless your physical union