2 years ago I worked with a couple. One day the male half of the couple approached me in a secluded area of our work and kissed me. I was confused as I wasn't aware that he found me attractive or wanted to kiss me, let alone that he thought he could just walk up to me and kiss me. To my re-collation I had never flirted with him or made myself available to him.
I did not push him off, but I don't remember kissing him back either. It was all very surprising and I was thrown off guard. He then stopped kissing me and asked me to come into a store room with him (classy). I declined and left the area. The next week the business closed unexpectedly and we never saw each other again so there were never any repercussions from the incident.
I have recently found out the couple have got engaged and I am in two minds whether to tell the girlfriend what happened. One part of me thinks if it were me and I were about to make a huge commitment, planned to spend my life with someone, I'd want to know if they had been disloyal to me during our relationship. Another part thinks, it was two years ago, it was probably a silly mistake on his part that he regrets and is glad never went anywhere. Another part thinks I would just look spiteful and trying to cause trouble for a happy couple which I am 100% not.
I know I will get hate for being the 'OW' but would I be unreasonable to tell her or should I just let them get on with things?