Hi TheDayDreamer,
Well first of all, have you met the ex? Sometimes old girlfriends are labeled as “Crazy” but they are actually normal. Now, yes, she’s had problems too deep for him to handle. But is she really manipulative?
If you haven’t met her, it’s easy for the mind to Fill in the Blank.
What I would do is say, “If you hang out with her, bring me along.” This way she won’t try anything and he won’t go back into their unhealthy dynamic.
If she asks him for lunch, he should say, “Let me see if my GF can make it.” If she pressures him to meet up with her alone he should say, “I’m busy.”
As far as texting/calling/Social Media: He should view her as “That Guy”. There is always “That Guy” in your group of friends. That you are friendly to but not actual friends with. A short, one line answer or one minute conversation at best.
Blessings,
Inky