At the risk of sounding harsh no-one here can possibly tell you what went wrong. You have to assess what failed in the relationship and figure out how to change your focus & vibration to get what you desire.
Sometimes the easiest part is using PW to get the person back, but sustain a high vibe and not letting doubts and fear enter the relationship can be difficult.
You got him back once so u can do it again, but take the time to remedy what went wrong within yourself.
I posted a little while ago my success story with my most current ex (J) under "It Works". Everything was great I used PW to get him to tell me he loves me and make us official. Originally I was using this technique on another ex (K), who broke my heart. Out of the blue he (J) broke up with me, he said he doesn't feel chemistry anymore and I haven't heard from him in 3 weeks. What happened? Im hurt but will continue RS on him. Also the ex I was originally doing this on has a new gf and is saying all the things on Facebook about her that I was visualizing him saying about me. It hurts, but I'm not letting it ruin me. I love them both. I just don't understand what happened? Any advice?