Go over to her fiance's house and kick the utter living shit out of him. How can you let him just steal your girl? You put in 5 years tapping that pussy, he has only put in 3 months. He is laughing at you right now man. He's sitting back while she blows him thinking "wow, that ex-boyfriend of hers really is a pansy, this bitch is blowing me every night and it didnt even take a month to get into her pants."
You need to get the upper hand back and the only way to do that is to fuck this guy up. I mean you gotta send this guy to the ER for major reconstructive facial surgery. He just stole the girl of your dreams, the girl you did so much with over the last 5 years. If he's gonna get her, then he needs scars for life so that everytime he looks in the mirror, he remembers the concequences of his actions. Dont be a fucking pussy. Man up.