Fiancé and female coworkers?

So my fiancé works in a small office and he has his own individual office room that’s pretty small, maybe about the size of the usual bathroom, I have not measured it obviously lol but it has enough room for his chair, his big desk and all his work papers and such. Him and his boss are thinking of taking on an intern, an intern that is my fiancé’s friends little sister who just graduated and wants to learn the ropes of a business. My fiancé is trying to help her out, which I think is a good thing. But the thing is they don’t have room for another office so she would work in the same small room my fiancé is in and they would share a desk. I don’t know how that’s gonna work because of the small space. It doesn’t sit well with me and I’m not sure why? Like obviously I don’t have a problem with him being around female coworkers but they are sharing a single desk in a small room for eight hours everyday. Like I wouldn’t be comfortable doing that with a male coworker I don’t think unless there’s other people around or a little more personal space. My fiancé is all for this and he’s encouraging the girl to come on with them.

Am I over reacting or should I bring it up to him that I’m uncomfortable?