Could say that it's sometimes difficult for you to dwell on the memories. Could mention that utilizing a counselor to work through the grief is helpful for many. Could say that right now, you're at a point in life where you need to step back.
Unfriending does seem a bit extreme. Maybe the more unavailable you become, the less they'll reach out. Could limit them from seeing much of your activities. Could disable chat. Maybe disable messaging in private?
Certainly sounds like they make it about them and aren't moving forward.