Seeing Someone?

PRE THOUGHT: If someone doesn't want to tell you they are seeing someone, what are the limits on how you are towards that person? Should I just keep as is and have limitless conversations and hangout with a man who doesn't want to reveal that information to me?….Because if he doesn't share it, how would I know any different? And when you first meeting someone, don’t you usually ask if they have a boyfriend or girlfriend?