Your close friend broke up with her boyfriend of three years about two months ago. You assumed they would get back together, but now he's hooked up with another one of your/her friends, and they've been going out for about three weeks. Your friend/his now ex-girlfriend is the only one in the group who doesn't know, and he is scared to tell her because he doesn't want to hurt her etc/she had suspicions that there was something going on between him and said friend whilst they were still together.
What do you think of this situation? Do you tell your friend that her recent ex is now dating your mutual friend? Why/why not?