How do you regain happiness?

how does one regain happiness and joy again? I am in the pre-divorce stage. Wife left for a strangershe met on the web. I never got closure nor have we spoken in3 mos. She apparently has moved on and is happy, I however am alone in a new state with no friends. I try doing things I enjoyed b4, but I done seem to find joy anymore since the freight train ran over me. I guess in part because I can't get what happened off my mind. How can one in my position regain heir joy for life after such a traumatic event?