Letting your ex wife know your social schedule may be desirable in your situation, but is not something you are obligated to do.
I would say that your method of telling her would correspond to your reason for telling her.
He is dating his ex wife Paige Braswell again.
You don't, unless someone you can trust tells you, or you see her. But, as she is your ex-, why concern yourself about it!
Tell your ex-wife to stay out of my daughter's love life.
Only if you are sure that you will never talk to your ex girlfriend again.
NO
Why does that matter
It is you that keeps the cycle going. 'Ex' means the relationship is over so all you have to do is tell your ex it is over, not answer emails, the telephone or have anything to do with them. Start dating again and the ex will get the message. If they are harassing or threatening you then call the police.
If you love your ex wife still and she is not steady dating anyone or has married again then it's worth a try, but only if you feel you at least have matured since the breakup and hopefully she has too. If you just want to see your ex wife out of curosity or just have a friendship don't make this mistake and move forward in your life.
tell him or her that the other person is much cuter
you tell her very gently that you are dating him. example: mom, i am very sorry, but i am dating your ex husband. i know you don't like him, but i do. i can make my own decisions now. again, i am very sorry. WHY ARE YOU DATING A MAN YOU HAD AS A STEP DAD! WHO MEANS MORE TO YOU YOUR MOM OR THE MAN THAT POSSIBLE BROKE HER HEART! LADY GET A CLUE THATS DEFINATELY GOING TO BACK FIRE ON YOU!
when you two start dating again
sure as long as you were technicly divorced