My fiancee called off the engagement?

My fiancee Dawn told me she can't marry me until she knows for sure i only love her. She told me she knows i still have feelings for my EX Wife Stacy and she can't be with someone who isn't 100% committed to her. it's no secret Stacy wants to get back together. She told me the divorce was a mistake and she knew i never wanted the divorce in the first place. She told me she never stopped loving me and our daughter would be ecstatic because she never understood the divorce. I did kiss Stacy recently but it was after a fight with Dawn and i was drunk. Part of me wonders what would have happened if we stayed together but the other part has moved on and wants to be with Dawn. What should i do?