I work with three colleagues in a small open space. We're developers. We've been colleagues for almost a year and got to know each decently.
I'm a shy, socially anxious person that doesn't have many friends. I would appreciate making new ones. I get along well with most people. So far, I maintained a friendly although a bit distant image to all of my colleagues.
I would like to break the ice with one colleague in particular (say Bob), who is the only I appreciate deep down. So I would like to invite him to have a drink or eat after work, bringing each other's partner.
The problem is, Bob isn't in my team, so he's not the one I socialize the most with, and my other two colleagues might get upset they didn't get invited. So far and for all that I know, afterworks were rare and strictly collective. We're in a close space and Bob is chatty, so I guess even if I did invite Bob privately they will soon or later learn I've (tried to) befriend Bob and not them, which I find embarrassing.
How could I deal with this situation in a tactful manner?