I only tell my co-workers what they need to know as concerns me professionally. Work is a funny place, as you will end up becoming closer to some people rather than others. The best rule of thumb is: If I tell person A about this, and they let it slip to my supervisor, or to anyone else I have to work with daily, how is that going to affect me at work? Trust issues at work should always be foremost in your mind, simply because they are people who would love to see you fall or fail, and for every person you can trust at work, there are probably three you cannot. Work isn’t a place for casual conversation, and if you let your guard down to the wrong person, it can come back to bite you in the ass. Keep your guard up, always. Better to be too closed mouthed than open minded. The number one product produced by any job in America is gossip.