Moon in cancer..... unforgiving.........?

my friend has a moon in cancer and sun in pisces... i told him how important he was to me and he said oh... i asked him why he said only oh and then he explained that this girl he had been very good friends with took advantage and hurt him and she used to keep telling him he's important so now when anyone says he's important he doesn't really believe it.. seems like he hasn't forgiven this girl and he feels like he can never be important to amyone.. i read his chart and when i read the description for cancer moon i realized that he's so emotional and stuff because of that.. what's the best way to help him??? he hasn't forgiven one girl and now thanks to that ***** he feels alone and like he can't matter to anyone..