Will you be okay with your husband business trip alone with a woman?

I want to know if I am paranoid but I am not okay with this. My husband has business trip with his colleague to Sydney. They are also extending to spend Saturday in Sydney, fly back Sunday morning. He says they are really just colleagues. But my spidey sense tells me that cannot trust. If you are in my shoes, will you find it acceptable? Should I ask to join in the trip!