THis is not a hard scenario to overcome.
Recognize your crush for what it is, a crush.
If you have deep seated reservations about your marriage, or some incompatible issues with your fiance, then that is a problem and it needs to be dealt with.
HOwever, as a man, if you find another woman attractive, then that is normal. But if you develop a crush on every woman you find attractive, then you better darn well get a hold of yourself because it won't be any different after marriage!
Never put any woman on a pedastal, and developing uncontrolled emotional crushes on this or that woman is doing just that very thing. THere are over 3 billion women on this planet, so the good man is wise to get control on how he "lets" any one woman affect him!
And especially this, you go to same university course, and same partys, same social circles, that is not an excuse.
Later, when you are in the workplace, working in close proximity with often attractive and available women for years, and on the same projects, etc, as a man you simply have GOT to establish concrete boundries on feelings for such women.
For myself, I put into place firm boundries that I simply will not flirt with women I work with, nor will I discuss with them anything relationship related, nor will I even be part of a conversation with a group of women socially concerning men, or concerning their husbands/boyfriends, or anything sexual or gender related.
The irony is, years ago since establishing that boundry, it is amusing to me to see how often when exposed to my aloofness how (especially the younger) women then trip over each other to dilberately and overtly try to engage my attention in such flirting or relationship small talk, so much I assume I am in a way the seduction community would define as "negging" them.
And yes, I admit, I find that MUCH MORE amusing than any misplaced crush feelings.
And I will close with this, drop the fear of your woman seperating your vegetables. It is important for her to know that you are capable of attracting, and being attractive, to other women. No woman wants to win and keep for long any man that is not a challenge, a prize worthy of being fought for and won.
And it is just as important for you to be both honest to your woman, and never afraid of your woman, for a man that is afraid of a woman, he will only sow his own seeds leading down the road to resentment and lack of respect from his woman!