I have to set up specific boundaries, too.
1. Don't touch them.
2. Listen for two minutes, then, "Gotta go." I would not give any personal info about what I'm doing these days and I certainly would not go into any of our past. I wouldn't offer up any suggestions on how they could help their situation.
3. I wouldn't say, "Nice to see you." I would try not to smile at them or act friendly. I wouldn't ask any questions. I would say, "I have nothing to say." Then walk away.
There are ways to shut down conversation. Women have Resting B Face. Maybe look that up.
