For me personally, when a mutually friend would bring up XA in conversation, I had to firmly state that I did not want to hear about him, it was no longer my business or concern. My true friends respected my wishes, found out the rest were just gossipy, and nosy.
It will get easier, keep yourself busy, when you feel yourself slipping down that slope, call a friend, read a book or magazine, cook, clean, go for a walk, go to the store, do anything not to fall into that mindset.........
It is sad to see the life we once shared end. Better days are on the horizon my friend, hang in there.
Peace.