I can't seem to have a conversation with this person without them saying something that opens old wounds, or invalidates how I feel. I no-longer see this person but we have been chatting on FB. Is it better to just stop chatting with them, or to just unfriend them?
If they make you feel that way, then it is best not to talk to them. You should find people to talk to who make you happy.
stop chatting, they'll get the idea. i've done the deleting thing and it feels good if you're 100% certain but halting communication seems to work just as well