Gleak, I think you aren't communicating very well with your girlfriend/fiance. You said,

"Though, I did ask her to make the decision - I simply meant that as a gesture for her to take it on herself to decline because I simply did not approve and she should have known that."

She cannot read your mind! You have to say, in words, exactly what you think and mean. You did a double message with the "you decide" when you didn't mean that at all!

I think you need to work on either trusting your girlfriend or your relationship isn't going to work ultimately. She's another person with her own life, etc. She has to make her own decisions, truly, and it was kind of her to ask your opinion but I think you did her a disservice not giving her your true opinion! What I quoted above amounts to a double bind, no matter which "half" she responds to, she can't win. She decided for herself as you told her to do and you're unhappy. If she had let you make the decision, that would have hurt her and her own life.