Happy How Does My Friend Learn To Move On And Be Happy From Different Sources?

How does my friend learn to move on and be happy from different sources? - happy

Comprehensive source of happiness my friend is this girl that I liked him in the past. A direct correlation between the situation with the girl and her happiness. It has also caused much pain (and vice versa) through their friendship. He finally admitted he would rather without them happy and if not very unhappy with it. However, he did not know how happy without them, and I no longer have any suggestions you, as my friend can overcome this friendship with this girl and to learn from different sources to be happy?