I would be surprised to find out that my dad or mom had really loved someone other than each other, before or after they married. I already know that both of them must have liked and been interested in another person, before they met on a double date...not with each other.
I would be more shocked than devastated, I think, if I found out that my dad had loved another woman in the way indicated, after they married. There were no kinds of signs, and their love for and commitment to each other was evident in many ways.