Am I wrong for not wanting my fiancée to talk to a guy she's attracted to?

A couple of weeks ago, my fiancée met a coworker who, she admitted, makes her feel "some kind of way" when he talks to her. I told her that crushes are normal and that throughout life, you’ll meet people you have chemistry with. I asked what she’d do if she developed a crush on him, and she reassured me that she’d stay with me no matter what.

Recently, I found out she was planning to hang out with him outside of work to study a shared interest. She was upfront about her intentions, which seemed innocent, and in the two years I’ve known her, she’s always been a very genuine and trustworthy person. But it’s been eating away at me because spending time with him outside of work feels like it could bring them closer.

I feel awful because I don’t want to limit her life experiences or connections. She’s really happy at home, and I do my best to keep her fulfilled—I cook, give her gifts, spend all my free time with her, and take her on new adventures. She doesn’t have many friends, even though she tries, and he’s been the one consistently giving her attention.

Update: I told her I was still feeling uneasy about the situation. She decided to cut off contact with him and won’t speak to anyone she feels chemistry with unless I’m okay with it. Thank you all for the thoughtful advice!