i agree a lot with what Amber said. There's usually subtle hints, but by the same token, he may not engage in those behaviors due to Oz's point. Honestly, if i were in your shoes, i would seriously think about establishing boundaries, this is workplace behavior, this is social behavior. In a social setting, he may be more willing to engage in those "inner Dom" behaviors so long as he's comfortable with the boundary. By the same token, i also agree that if you don't want a vanilla relationship, then just come out and ask. Or maybe just tell him what you're into and see his reaction. Many good points here, it's hard to choose the best option.