Is it necessary for immediate boss to know you are a divorcee?

It is not necessary at all for any boss to know your personal matters. in fact many bosses are biased and will discriminate depending on personal matters that jobs do not depend on. Best keep it to yourself. If a boss specifically asks if you are married, consider the circumstances to see if it's relevant. If it's in a flirty conversation maybe he's checking you out to see if you're single. If it's not in a social situation, it's definitely not relevant and you can politely say that currently you aren't married.