I'm suspicious, I don't want my fiance to go out and drink alcohol with a work friend
Do you have any reasons for that?
A lot of reasons, but the main reason is that I don't like this guy.
This seems like a rough situation, if you think the co workers, that's one thing but if you don't trust your fiance that's another. Coworkers often go hang out, that is normal. Also, you don't control your fiance life, so you need to find a balance.
What do you mean? She can do what she wants.
She definitely can hang out with her coworkers, and it's good you accept that. However, don't you feel like you should try to trust her a little more? Work and life can have a great balance, and talking about this problem to her can help her reconsider to fit your feelings without you controlling her.